These are Oregon's Power Mate rim sprockets for chainsaws. Rims float on the splined hub of the drum and move side to side, allowing the chain and rim to align with the bar as the chain travels around the bar's groove. The rim gets most of the sprockets wear, and by being replaceable, it extends the overall life and value of the sprocket system. The rim also has wear depth indicators which tell you when to replace your rim. With standard splined rims have a sprocket bore of approximately 3/4". This rim is a .325 x 8 tooth configuration.
