Hi, I am building a bike for a friend and need to source another of these doodads:




What the hell are they called?

Can't find them on eBay or Amazon because I'm not sure what to call them. I've tried dropout adjuster, dropout limiter, dropout insert and dropout hardware, all of which turn up other parts or nothing at all.

Also, I know that these parts are used to seat the rear axle correctly in a horizontal dropout, on a bike with derailleur gears, but beyond that I'm mystified as to their specific purpose. Sheldon Brown has nothing. Anyone know more?

Thanks and happy riding!