A two-pound dead-blow hammer, often mistaken for a rubber mallet. The primary tool of the hacks at Orange County Choppers, especially Paulie. Chiefly used for axle installation, engine/transmission alignment and primary cover installation.
Properly used, an OCC wrench is a useful tool that one occasionally needs for stubborn, rusty old parts, not shiny new ones that should slide together if one knows what they are doing.
I have been a motorcycle mechanic for ten years, and have never needed the OCC wrench to put in an axle.
Look, that idiot Paulie dinged that primary with the OCC wrench!