The entire assembly. I had once thought of purchasing a bbr kick arm with the yamaha knuckle. But, Yamaha lists the knuckle seperately on their parts fiche - but no longer sells it seperately.
A friend had to put a small shim behind his yz kicker to space it out a tad. This was to get it to clear the crd frame guards - others just bolt it on...
To prevent (or sometimes repair) the oem kickstarter from "folding back" - one can drill and tap a steel screw where the aluminum contacts the steel knuckle. Use a thread locking agent and then grind the screw off flush after installation.
jeff