The 3/8-8 chain wheel, a drive sprocket for a chain trimmer head. The face is stamped 3/8-8, 3/8 chain pitch with 8 flat teeth, the flat teeth biting the chain, the chain running around the head's plane. A splined center bore meshes the machine's shaft, spline to spline with the nut on, and the shaft turning the wheel without slipping. A ring of lightening holes on the back, the wheel lighter, less load on the shaft and bearing, steadier at high speed. Stamped steel, standing up to wear and rattling. Swap it when the flat teeth are worn to points, the chain skips, the spline is round, or the face is cracked. The 3/8-8, 3/8-9 and 3/8-10 are one family, choose by the old wheel's stamping, and fit is not guaranteed for every one, so comparing against the old wheel is the safe way.

 FAQ 

Q1: What does the 3/8-8 marking mean?

The 3/8 is the chain pitch and the 8 is the tooth count. The 3/8-8, 3/8-9 and 3/8-10 are the same family, all biting the 3/8 grade chain, so buy the same number the old wheel's face is stamped with.

Q2: Is it a chainsaw sprocket?

No. A chainsaw rim sprocket has teeth on the edge for the bar chain. This one has flat teeth on the face for a chain trimmer head, the chain running around the head's plane, driven from the center.

Q3: How do I check fit before ordering?

Compare the tooth count, the spline shape and the face thickness on the new wheel with the old one. It is not guaranteed for every head, so checking against the old wheel is the safe way.