Since I upgraded my clutching I have no use for 2 new belts . They fit a stock 600 . They might fit a 503 , but not sure . I have 2 Carlisle ultimax 3 belts # 138-4628U3 . $ 110 for both shipped . I think they are about 82 each retail .
for all hawk owners info I ck. on the drive belts for all sizes and they all use the same belt. the 503 lists a different # in manual but it converts to the same carlisle belt # that is used on the 6&8. sugested list for these belts is 80.00.