What model and year Rocket III do you have?
Note that
Identical aftermarket peg mounts TO FIT SAME 11/4 INCH BARS ARE AVAILABLE FROM EbAY FOR LESS THAN HALF tRIUMPH PRICE The eBay ones have a shorter peg stem but if you use longer Allen head bolts they work fine with the Triumph accessory h'way pegs. That is what I'm doing with my Chromeline ones matching the rest of my Chromeline footboards and foot control rubbers
ADJUSTABLE HIGHWAY PEG MOUNT A9750455
Can only be used in conjunction with Dresser Bars A9758099
Have you got the h'way pegs yet?
Two Triumph styles to choose from,
the logo version are more expensive than the Chromeline:
HIGHWAY PEGS, LOGO - CHROME A9750459
For use with either
A9750455 or A9750463
Mounting Kits A9750523 Chromeline Highway pegs
SHORT HIGHWAY PEG MOUNT A9750463
Can only be used in conjunction with Dresser bars A9758099