Oregon Guide Bars

A well-designed, reliable guide bar is crucial to your chainsaw's performance. Oregon is a brand you can trust to get even the most difficult jobs done.

FAQ

FINDING COMPATIBLE SAW CHAIN

Determining Guide Bar & Saw Chain Compatibility

In order to figure out if the Guide Bar and Saw Chain you plan to use together are compatible, there are (3) key specifications that you must match up:

(1) Pitch, (2) Gauge, and (3) Drive Link Count.

Your bar and saw chain must have the same exact specifications, otherwise they will not work together. Please see the rest of this guide, and/or utilize the in-page navigation links to determine how you will find these exact specifications.

FYI, many retailers call out the length of the saw chain (in inches) as a starting point for customers, but please be aware: determining compatibility solely by length is the most common reason we see for incorrectly ordered saw chains. While a saw chain and guide bar may be the same length in inches, the rest of their specs (Pitch, Gauge, or Drive Link Count) may differ, making the pair incompatible. Again, the only specifications you really need to ensure compatibility are Pitch, Gauge, and Drive Link Count of both your guide bar and saw chain.

Measuring Your Chainsaw Chain

We'll let you in on a little secret. There are two ways that you can figure out the size of your replacement chain even without access to a product manual:

Measure the chain yourself, using instructions below.
Look on other parts of the saw for the measurements, most likely on the guide bar OR on the drive links of your saw chain (easiest options).

How to Measure Chainsaw Chain Yourself

To find a chain replacement, you'll need to figure out three numbers:

Pitch: the distance between the chain's drive links
Gauge: the width of the groove where the chain fits into the bar
Drive Link Count: # of drive links contained within the loop of chain

Measuring Pitch

Chain pitch is the length of the links in the chain. To determine the pitch, you'll need to measure the distance between any three consecutive rivets, then divide the result by 2. The rivets are the small, round pegs/studs that hold the chain segments together. Measure from the first to the third, then divide that number in half to get your chain pitch. Pitch is important because the drive sprocket (and if applicable, the bar nose sprocket) of your guide bar must be the same pitch as the chain.

The most common measurements of pitch you'll see on replacement chain are 3/8" and .325", but may also be .325” Low Profile, .404”, ¼”, ¾”, or ⅜” Low Profile.

Measuring Gauge

Chain gauge, on the other hand, means the thickness of the drive links of the chain. Your saw chain’s gauge can be determined by measuring the portion of the drive link that fits into the groove of the guide bar, usually expressed in thousandths of an inch. For your reference, normal wear can make it difficult to accurately measure chain gauge on a worn chain.

The most common saw chain gauge sizes are .043" (1.1mm), .050" (1.3mm), .058" (1.5mm), and .063" (1.6mm), but may also be .080” or .122”.

Measuring Drive Link Count

Count the number of drive links on your old chain loop to get the correct replacement chain. Simply count the drive links around the entire loop of saw chain. The drive link count is the last 3 numbers before the last letter on the Oregon chain part number.

For Example, 72LGX072G = 72 Drive Links; 18HX078E = 78 Drive Links.

Where to LOOK for Measurements on your Saw Chain

Your old saw chain (that you are replacing) may also contain all the info you need, as the type of saw chain is typically stamped right onto the drive links. The specific saw chain type will provide you with the Pitch and Gauge. For your reference, Stihl uses an extra marking on the tooth link to determine size.Please view the different brands’chain codes, their meanings, and brand-to-brand conversions to Oregon saw chain, below. Once Pitch and Gauge are figured out, all that’s left to do is count and match up the drive links.

Oregon Chain Families: Understanding the Differences

We understand that the needs of woodcutters – professionals and novices – are as diverse as the terrains and environments in which they work.

Oregon has organized their saw chains and guide bars into product families with key characteristics that different users will value. These product families will ensure that you choose the right chain and bar based on your everyday needs. It will make understanding the differences between our products effortless. Feel free to click on the titles below to see our company's saw chain offerings.

POWERCUT
The ultimate saw chain for loggers and skilled forest workers who use high performance saws. Full chisel cutters power through timber with speed, efficiency, and precision.
SPEEDCUT & SPEEDCUT NANO
Faster cutting performance for wood-cutting professionals who use mid-size saws under 55 cc. Narrow kerf system requires less power to cut through high volumes of wood quickly and easily.
CONTROLCUT
Ideal for wood cutting professionals looking for a fully featured cutting system that delivers smooth cutting and reduced kickback. Easy to maintain saw chain, with a forgiving sharpening profile.
RIPCUT SPECIALTY CHAIN
Ripping chain created specifically for chain-type sawmills. Produces smooth ripping cuts with supreme efficiency to make precise boards and planks.
POWERSHARP
Easy-to-use, precision sharpening system that gives chainsaw users the power to sharpen their chain in a matter of seconds with a simple attachment. Patent protected features make PowerSharp a major advance over other sharpening methods.
SCULPTOR SPECIALTY CHAIN
Easy to maintain and light-weight for optimum maneuverability. It is the perfect tool for carvers, pruners, and any other user who values extra-fine cutting.
ADVANCECUT
Perfect for homeowners or landscapers who occasionally need to cut trees. The low kick-back design makes it easy to get great results, even if you don’t wield a chainsaw every day.
VERSACUT
Designed for landowners and tree-cutting professionals who require a multi-purpose, high performing saw chain. Uses cutters designed for maximum durability and versatility.

FINDING COMPATIBLE GUIDE BAR

Determining Guide Bar & Chainsaw Compatibility

In order to figure out if the Guide Bar and Chainsaw you plan to use together are compatible, you will need to determine (3) key specs for your chainsaw:

(1) “Required Bar Mount,” (2) Pitch, and (3) Gauge

By definition, replacement bars that are interchangeable with the original bar are those that both fit your saw (bar mount and pitch) AND take the same type of chain (pitch and gauge).

In practice, there are several different mount, pitch and gauge combinations in use - even in the chainsaws and bars of a single manufacturer - meaning most guide bars are mutually incompatible. Please view the rest of this guide to learn best practices of finding this info yourself.

Measuring Your Guide Bar

Bar Length

Many retailers call out the guide bar's length as a starting point for customers.

While the guide bar length isn’t always necessary to know when trying to determine compatibility, it will help us narrow down what size of bar you’re looking for.

You'll be measuring the usable length of the bar, also called the cutting length, or the called length.

To find the called length of your chainsaw bar, measure it from its front tip all the way back to the cutter closest to the body of the saw.

Round this measurement up to the nearest inch. For example, a bar that measures 19 3/4" will actually have a called length of 20".

You then could look for a new bar with a 20" bar length.

Bar Mount

Most chainsaw bars use a superficially similar arrangement of slots and holes for mounting to the chainsaw body. This arrangement is called bar mount (or tail mount). To be compatible, a guide bar and a chainsaw must have a matching bar mount type.

Notice in the photo below the many variations that bar mounts can be oriented. Size and relative location varies between brands and also product lines of a given brand. Sadly, small differences make mounts incompatible: if the holes do not line up, the bar won’t fit or won’t work properly.

To make it easy, we only sell Oregon-brand guide bars. Each chainsaw brand/model will utilize one Oregon bar mount (possibly two, depending if the “old” bar mount has been discontinued/superseded by a newer one).

If you are replacing an old Stihl or Husqvarna guide bar, please take a look at our bar mount conversions below to determine which Oregon bar mount you will need for your chainsaw.

Converting Your Bar Mount to Oregon's Bar Mount

Oregon has dozens of bar mount variations that are used to accommodate an array of different chainsaws and brands. Oregon’s bar mounts are indicated by the last 4 digits of the part number (one letter followed by three numbers). For example, the Oregon 200RNDD025 would utilize bar mount D025.

Depending on the brand and age of guide bar you use, you'll most likely be able to find your guide bar's bar mount by looking at the part number, guide bar etching, or online using your chainsaw's Brand and Model #.

***If you have trouble finding this info for yourself, please reach out to us with your chainsaw's Brand and Model. We understand this can get quite confusing.***

Please view some of the common Stilh/Oregon & Husqvarna/Oregon Bar Mount Conversions, below:

Stihl bars use three types of bar mounts that can be determined by looking at the first 4 digits of the guide bar part #, usually etched into the guide bar itself:

“3005 - small” (converts to Oregon’s A074);

“3003 - medium” (converts to Oregon’s D025);

“3002 - large” (converts to Oregon’s E031 or E099).

Husqvarna uses two bar mounts that can be determined by the model number of the chainsaw you're using:

“small” (converts to Oregon’s K095)

“large” (converts to Oregon’s D009).

Where to LOOK for Measurements on your Guide Bar

Your chainsaw’s guide bar may have all the information you are looking for stamped right into it. It can usually be found near the back of the bar, where it mounts to the saw.

For instance, in the example above, the chain is 3/8” pitch and .050” gauge with 72 drive links. This, along with the bar mount conversion from above, should be all the information you will need to get the proper replacement guide bar.

Oregon Guide Bar Families: Understanding the Differences

We understand that the needs of woodcutters are as diverse as the terrains and environments in which they work. We’ve organized our guide bars into product families with similar characteristics to help you find the right guide bars for your work.

POWERCUT
For loggers and skilled forest workers who require heavy-duty guide bars. The tough chrome-moly steel body powerfully cuts through timber quickly and efficiently.
VERSACUT
Designed for landowners and tree-cutting professionals who require versatility without sacrificing strength. Switch easily from pruning to felling without changing saws.
CONTROLCUTIdeal for woodcutting professionals who make precise and smooth cuts during their work day. This guide bar’s lighter weight reduces operator fatigue.
DURACUT
Designed specifically for woodcutting professionals who work in challenging and punishing environments. The ultra high-wear resistant stellite nose and chrome-moly body gives you the power to cut through any challenging terrain.
ADVANCECUT
Perfect for homeowners or landscapers who need a reliable guide bar that is light-weight and maneuverable. The bar is also designed to reduce kickback.
SINGLE RIVET
Designed for homeowners who need a light-duty bar for limbing and pruning. The bar offers users greater control, reduced kickback, and it is reversible.
SPEEDCUT & SPEEDCUT NANO
For woodcutters who cut high volumes of wood. Narrow kerf, light-weight, and ideal for professionals who need mid-sized bars for saws under 55cc.
HARVESTER
A harvesting machine is only as good as its cutting attachments. That’s why discerning users choose Oregon Harvester Bars. Their harvester bars make your wood processing machine rise to its potential - maximizing your cutting efficiency while minimizing your down time.

SAW CHAIN MAINTENANCE

Chain Maintenance

Sharpening Your Saw Chain

If your saw chain is no longer self-feeding, you have to push on the saw, or the waste material from your saw creates sawdust, it is time to sharpen your chainsaw chain. A good rule of thumb is to sharpen your chain every time you refill gas.

Please view the video below to see how Oregon recommends sharpening saw chain with files:

Please view the videos below to see how Oregon recommends grinding saw chain with their 520-120, 620-120, 410-120 Bench Grinders, as well as their Sure Sharp Mini Grinder. Please use the video time-stamps to jump to the section of the video that you need.

Determining the Correct File to Use for Your Saw Chain

There are a handful of file sizes that are each meant to sharpen different saw chains, determined by the Pitch of the saw chain. In order to determine the correct file for your needs, you would need to locate the Pitch of your saw chain by using one of the methods mentioned above: finding the code on drive links, etching on bar, or directly measuring the saw chain.

If you have determined the pitch of your saw chain, this table above can be used quite universally with most brands of saw chain.

However, there are some key notes to be careful of when determining the right file:

Round files go only with round grind teeth. If you notice straight sections and multiple angles on the cutting edge, check the specific filing instructions for that chain model.
Regular and Low Profile Saw Chain require different size files. 3/8” and 1/4” Pitch chains come also in Low Profile (Picco) versions, which have lower cutters and take a smaller file.
Manufacturer recommendations vary from time to time, meaning it's always worth it to check your specific saw chain’s manufacturer recommendation. ***Sometimes intermediate sizes, 11/64” and 13/64”, are recommended instead of the XX/32” sizes.***

File Size Conversions by Popular Brands

Please view the recommended file sizes for common Husqvarna saw chain and Stihl chainsaws, below:

Filing and Grinding Sizes/Angles for Oregon Saw Chain

If you are filing/grinding a saw chain other than Oregon, please use the saw chain converters above to determine the correct angles for your saw chain. Grind your chain so that it meets the recommendations of the manufacturer.

Saw Chain Lubrication

Fill your oil reservoir each time you fill your chainsaw’s gas tank. Make sure that your saw chain, guide bar, and sprocket are always receiving oil from the saw during operation.

Keep your saw's chain-oiling system filled with clean bar and chain oil. Oregon bar and chain oil is specifically compounded to provide extra high tackiness and prevent "throw off" even under adverse weather conditions.

As a rule of thumb, you should never put used oil or old motor oil in your saw or on your chain. Used motor oil contains metal shavings that reduce the life of your bar and chain. Additionally, lubricating your bar and chain with used motor oil will void your warranty.

Tips for Dealing with Cold-Weather Wear

Oil

Use a lighter weight of bar-chain oil, or dilute bar-chain oil 25% with clean kerosene or diesel oil (you’ll need to use twice as much of the diluted oil) and be certain your chain is receiving oil from the saw.

Cutters

Keep cutters sharp.
Touch up every hour, more often if needed.
Do not force dull chain to cut.

Bar

Turn symmetrical bars over to equalize rail wear.
Keep the bar groove clean and oil holes open.

Tension

Check and adjust often.
Keep your chain correctly tensioned.

Depth Gauges

It's recommended to check the bite of cutters is regulated by the height of the leading portion of each cutter, commonly known as the depth gauge.
Check and adjust your cutter's depth gauges at every sharpening.

Drive Sprocket

Be sure to read the operator's manual supplied with your chainsaw in its entirety.
Replace the sprocket after every two chains, or sooner if wear is evident.

GRANBERG ALASKAN SAW MILLS

MAKING LUMBER

Download PDF Here!

CHAINSAW POWER REQUIREMENTS

In general, you will need at least 50cc to run our smallest mill (G777). The more powerful your saw, the easier your milling experience is going to be. Consult the chart to see if your chainsaw has enough power to do the job you want it to do. Under-powered saws will take longer to make a cut and may overheat and possibly fail. You will definitely want to use a ripping chain and take your time. Granberg will not take responsibility for damage caused by using saws that are under-powered. We also recommend against using battery or electric saws.

WEDGING TECHNIQUES FOR USE WITH MILLS

It's important to have proper wedges. Depending on the size of the log you are milling, the weight of the slab or beam may be pinching the chain. Using wedges as you move through the cut can help lift the wood out of the way. Wedge early, wedge often. You can buy some on our website here if you don't have any at home.

A good wedge is at least 6″ long, 3″ wide and tapered from 3/4″ to 0″. Best to put at least 5 in your back pocket or tool pouch. After you cut into the log, about 2 feet, put the first wedge into the beginning of your cut. Then put a wedge in every two feet.

Larger, thicker slabs require more support, meaning use more wedges and tapping them in really well.

Lighter, smaller slabs require less support, meaning use less wedges and giving just a quick tap.

CAN I PUT A LARGER MILL ON A SMALLER BAR?

Yes, all of the Alaskan mills we carry can be adapted to fit a smaller bar, because the thickness rails have a channel all the way down that will allow the depth post to be moved. So, if you have a 32” bar, you will want a 36” mill (G778-36). The nose end depth post can be adjusted down to fit the smaller bar.

Likewise, if you have a 36” bar at the moment, but are maybe thinking about investing in a larger bar, you can buy a 48” mill (G778-48) and put it on the smaller bar until you get the upgrade.

One consideration you will have to make is although you can put a larger mill on a smaller bar, the mill size itself will not change, so you will need enough room to operate a 48” mill even if you are only using a 36” bar. This is really only an issue in the thickest of brush. If you’re milling in your driveway or front yard, you shouldn’t have a problem.

MILLING TIPS FOR FIRST TIME USERS

Learn from Mr. Erik Granberg, President of Granberg International the tips and tricks to getting the best results from your Alaskan Chainsaw Mill.

VIDEO RECAP

1. THREE important things to consider before milling. One, does your chainsaw have enough power? (see bar/power reference chart). Two, ripping chain is necessary! Three, a first cut system to assist in your first cut. (0:35)

2. Inspect log and debark. Check diameter of log vs the cutting width of mill. Is your mill going to make it through the cut? There may be a section that is too wide. This can be trimmed before milling. (2:00)

3. Mount Alaskan Mill onto bar. Adjust to fit bar. Avoid clamping down on the sprocket nose. Tighten all hardware. The clamping bolts for the bar and end bracket require 10-12 pounds of torque. Tighten evenly. All other carriage bolts use 8-10 pounds of tightening torque. Do not over tighten, this only weakens the bolts. (3:15)

4. Tool kit check. (11:07)

5. Safety Equipment. Chaps, gloves, boots, eye and ear protection are required! (11:51)

6. Make sure your wedges are handy! (12:20)

7. Best way to start your second cut. (13:17)

8. Wedging tips while milling. (14:18)

9. What to look, listen and feel for while milling. (14:54)

10. How to exit the cut. To keep the mill from dipping when exiting cut, put a little back pressure on upright handle and support the powerhead. (17:24)

ARBORIST ROPE CARE

SELECTING the Rope

Selecting a rope involves evaluating a combination of factors. Some of these factors are straight forward like comparing rope specifications. Others are less quantitative like a preference for a specific color or how a rope feels in your hand.

Fiber and construction being equal, a larger rope will outlast a smaller rope, because of the greater surface wear distribution. By the same token, a stronger rope will outlast a weaker one, because it will be used at a lower percentage of its break strength with less chance of overstressing.

Consider the opinion of professional climbers who may have more experience as to how well a rope performs. Consider also the reputation of the rope manufacturer. Are they involved with and supportive of the arborist industry? Do they stand behind their products with consistent quality and reliable service? Buying unproven ropes because they are a little less expensive is false economy and can lead to disaster

Some things to consider when looking at ropes are:

Strength
When given a choice between ropes, select the strongest of any given size. A load of 200 pounds represents 2% of the strength of a rope with a breaking strength of 10,000 pounds. The same load represents 4% of the strength of a rope that has a breaking strength of 5,000 pounds. The weaker rope is having to work harder and as a result will have to be retired sooner. Braided ropes are stronger than twisted ropes that are the same size and fiber type.
Elongation
It is well accepted that ropes with lower elongation under load will give you better load control, a big help at complicated job sites. However, ropes with lower elongation that are shock loaded, like a lowering line, can fail without warning even though it appears to be in good shape. Low elongating ropes should be selected with the highest possible strength. Both twisted ropes and braided ropes are suitable for rigging. Twisted rope has lower strength and more stretch. Braided rope has higher strength and lower stretch.
Firmness
Select ropes that are firm and round and hold their shape during use. Soft or mushy ropes will snag easily and abrade quickly causing accelerated strength loss. Because the fibers are in a straighter line, which improves strength but compromises durability, loose or mushy rope will almost always have higher break strengths than a similar rope that is firm and holds its shape.

USING the Rope

Proper use of your ropes, maintaining them, and staying within recommended working loads will allow you to get the most from your rope investment. Working loads are calculated to maximize safety and extend the working life of both climbing and rigging lines. Dirt and grit embedded in the fibers can also significantly shorten rope life. Keep them clean, bagged and properly stored when not in use.

Working Loads
Working loads are the loads that a rope is subjected to in everyday activity. They are normally expressed as a percentage of new rope strength and should not exceed 20% for rigging lines and 10% for climbing lines. A point to remember is that a rope may be severely overloaded or shock loaded in use without breaking. However, damage and strength loss may have occurred without any visible indication. The next time the rope is used under normal working loads the acquired weakness can cause it to break. Do not blame the rope, it was simply overloaded and failed from what is known as fatigue.
<img src="https://cdn.shopify.com/s/files/1/0576/5591/8746/files/workloadlimits.png?v=1673980336" />

Shock Loads
Shock loads are simply a sudden change in tension – from a state of relaxation or low load to one of high load. Any sudden load that exceeds the work load by more than 10% is considered a shock load. The further an object falls, the greater the impact. Synthetic fibers have a memory and retain the effects of being overloaded or shock loaded and can fail at a later time, even though loaded within the normal working load range.
Cleanliness
Modern arborists ropes often have 12, 16, or even 24 strands of fiber bundles making up their constructions. Dirt and grit can work their way in between the strands where they act like tiny knives. As the rope flexes, the grit and abrasives can act like tiny knives, cutting away at the strands of the rope from inside. This is why it is important to keep your ropes as clean as possible, especially if you are working in an area with lots of sand or grit. A brush tarp or rope tarp laid out at the base of the tree to pile the rope on is a great way to keep it clean. Better still is deploying the rope directly from an arborist rope bag. This ensures that the rope stays as clean as possible, and also helps prevent tangles and snags. View our selection of rope bags here. Ropes can also be washed, either by hand in a rope washer or by placing it in a mesh rope-washing sack and washing it in a front-loading washing machine with a gentle detergent or Rope Soap. Chemical solvents or abrasive cleaners should NEVER be used on an arborist rope. Always let your ropes dry before storing them to prevent mildew and mold.

RETIRING the Rope

One of the most frequently asked questions is “When should I retire my rope?” The most obvious answer is before it breaks. But, without a thorough understanding of how to inspect it and without knowing the load history, you are left making an educated guess. Unfortunately, there are no definitive rules nor industry guidelines to establish when a rope should be retired because there are so many variables that affect rope strength. Factors like load history, bending radius, abrasion, chemical exposure or some combination of those factors, make retirement decisions difficult.

Inspecting your rope should be a continuous process of observation before, during and after each use. In synthetic fiber ropes the amount of strength loss due to abrasion and/or flexing is directly related to the amount of broken fiber in the rope’s cross section. After each use, look and feel along every inch of the rope length inspecting for damage as listed below:

Abrasion
When the rope is first put into service, the outer filaments of the rope will quickly fuzz up. This is the result of these filaments breaking and this roughened surface actually forms a protective cushion and shield for the fibers underneath. This condition should stabilize, not progress. If the surface roughness increases, excessive abrasion is taking place and strength is being lost. As a general rule for braided ropes, when there is 25% or more wear from abrasion the rope should be retired from service. In other words, if 25% or more of the fiber is broken or worn away the rope should be removed from service. With three-strand ropes, 10% or more wear is accepted as the retirement point.
Glossy or Glazed Areas
Glossy or glazed areas are signs of heat damage with more strength loss than the amount of melted fiber indicates. Fibers adjacent to the melted areas are probably damaged from excessive heat even though they appear normal. It is reasonable to assume that the melted fiber has damaged an equal amount of adjacent unmelted fiber. Unlike fiber compression, melting damage cannot be mitigated by flexing the rope. Melted areas must be cut out and rope respliced or the rope must be retired
Discoloration
With use, all ropes get dirty. Be on the lookout for areas of discoloration that could be caused by chemical contamination. Determine the cause of the discoloration and replace the rope if it is brittle or stiff.
Inconsistent Diameter
Inspect for flat areas, bumps or lumps. This can indicate core or internal damage from overloading or shock loads and is usually sufficient reason to replace the rope.
Inconsistent Texture/Stiffness
Inconsistent texture or stiff areas can indicate excessive dirt or grit embedded in the rope or shock load damage and is usually reason to replace the rope.
Temperature
When using rope, friction can be your best friend or worst enemy if it is not managed properly. By definition, friction creates heat, the greater the friction, the greater the heat buildup. Heat is an enemy to synthetic fiber and elevated temperatures can drastically reduce the strength and/or cause rope melt-through. Each rope’s construction and fiber type will yield a different coefficient of friction (reluctance to slip) in a new and used state. It is important to understand the operational demands and ensure the size, rope construction and fiber type be taken into account to minimize heat buildup.
<img src="https://cdn.shopify.com/s/files/1/0576/5591/8746/files/RopeTemps.png?v=1673983985" />

Volume Reduction
Rope displaying 25% strand volume reduction from abrasion – rope should be retired from service. Amount of volume reduction that indicates retirement depends on rope construction. Refer to “check list” below:
<img src="https://cdn.shopify.com/s/files/1/0576/5591/8746/files/RopeVolumereduction.png?v=1673983925" />

Flat Spot
Rope displays a snagged strand. If the strand can be worked back into the rope, no need to retire. If not, this indicates a retirement point.
Cut Strands
Rope displays two adjacent cut strands. This rope should either be retired or the cut section should be removed. If possible, re-splice. Number of cut strands that indicate retirement depends on rope construction. See “checklist” below:
<img src="https://cdn.shopify.com/s/files/1/0576/5591/8746/files/Rope_Cut_Limits_b64dc83e-f656-405c-b8b5-5fe4c3a7d257.png?v=1673984417" />

ARBORIST BLOCKS/PULLEYS

There are dozens of pulleys and blocks available for the use of arborists today. However not all are created to the same specifications, and there are many applications which will put high demand on the hardware and for which only certain blocks should be used. While the terms "block" and "pulley" are largely interchangeable, we have divided them into two main groups for clarity:

Blocks
Built for tree rigging, including negative blocking - sustain shock loading a situation where the load free-falls momentarily before being caught by the block. This places far more force on the hardware than normal lowering, therefore only arborist blocks should be used in such situations. Arborist blocks have widened cheek plates to protect the rigging line from abrasion against the tree. Arborist blocks also have an upper sheave to safely attach a rigging sling. See our collection of Blocks Here.
Pulleys
Built for many purposes, not ideal for negative blocking - excellent tools for lowering static loads. They are not manufactured to handle shock loading and for these reason are often cheaper than arborist blocks. The relatively narrow cheek plates on a pulley may expose the rope to abrasion, so care should be taking that the line does not rub against the tree when rigging with a pulley. Most pulleys have carabiner holes in the upper body rather than an upper sheave, and so the rigging sling can not be tied directly to the pulley, and a shackle or clevis is necessary for safe operation. See our collection of Pulleys Here.

Other factors to consider when choosing a block or pulley are:

Rope Diameter Capacity - Blocks may be safely used with rope sizes up to the max. diameter capacity.
Sheave Diameter - The wider the sheave diameter, the less it will reduce the breaking strength of the rope or sling.
Working Load Limit (WLL) - Working Load Limit is the maximum load the block is intended to handle. The percentage of breaking strength that constitutes the WLL is different from one manufacturer to another, but is generally 20 -25%.
Breaking Strength (Brk Str) - This is the weight at which the device fails under test conditions.
Bearing vs. Bushing - Bearings are more expensive than bushings, but are more efficient and are sealed against dirt and sawdust. In practical terms, they have identical strength properties.