This brake is on the front end of a 61 Triumph,I just picked up. Serial number is an H18XXX which makes it either a 500 or 350 (can't figure out how to tell if it's a 350 or 500 either). Anyone have any idea what it's really from?

[Linked Image]

Cleared m out....left only
59 BSA Bantam (Trials)
78 Triumph Bonny (UPS)
02 Suzuki GS500