Grizzly YFM600 98-00. Raptor, Grizzly YFM660 01-05. This is the petcock lever gasket for many Yamaha motorcycles. It is reference #15 in the picture. Yamaha Part #3AJ-24534-01-00 supercedes Yamaha Part #3AJ-24534-00-00.
Only needed the o-ring to freshen up the stock petcock. Could have bought whole new assembly from Chinese manufacturer for a few bucks more but why do that? I should get 15 more years out of the original.