119471H, Case Hardened HD flat or plain washer for disc/drum brake mounting, they are a 5/16" id washer that is 0.080" thick
These are specially hardened by us, this is the correct way of mounting brake discs or drums (especially Alfins) so they don't 'bevel' around the capscrew or nut.
We also keep the STD thick 119471 plain / flat washer in non hardened state at a cheaper price of course