100961X Oregon Power Mate Rim Sprocket System

100961X Oregon Power Mate Sprocket System.  Fits Stihl 017,  018,  019,  021,  023,  023C,  025,  MS 210,  MS 210 C,  MS 210 C-BE,  MS 250,  MS 250 C,  MS 250 C-BE.  Pitch: .325", Size: Small 7 Spline, Tooth Count: 7.   Two-piece design includes a drum with a replaceable rim, allowing rim to be replaced multiple times before the entire unit is replaced. Extend operational life by maximizing chain and bar groove alignment. For best performance, replace every three rims.