This genuine Stihl helical spring provides the tension needed for proper bump line feeding action on compatible string trimmer heads. Part number 0000 997 2100 is for use on Stihl AutoCut 10-2, 11-2, 20-2 and 21-2 string trimmer heads.
String Trimmer Heads: AutoCut 10-2, AutoCut 11-2, AutoCut 20-2, AutoCut 21-2