Kickstarter crank

The 57-2173 is the kickstarter crank that lives on the gearbox outer cover, the arm the kickstart lever bolts to that turns your foot's push into motion at the mainshaft. It's a Triumph part, and the catalog books it under the GEARBOX OUTER COVER figure across a long run of appearances from 1969 through 1985, so it's a piece that stuck around largely unchanged for a long stretch of production. The older book form of this same part number is T2173, so if you're working from an early parts list and see that reference, it's the same crank.