3 OEM genuine Stihl 0000 642 1240 Clutch Drum Rim Sprockets 3/8-7 3/8 Low Profile Picco Pitch 7 Tooth, .675 ID.  
MS7 spline.  

Rim sprocket 3/8'' Picco 7T
Genuine Stihl Part
OEM Part No. 0000 642 1240

Spline Size Mini 7 Spline (MS7)
Bore (.675")
Diameter  (1.433")
Important Note *MS7 Mini 7 Spline Rims have an interior diameter of approximately .675" (less the splines) and will only fit clutch drums with that diameter bore. Please check before ordering.