Your shifter fork that attaches your transmission to your shifter is held onto the transmission by 2 bushings, one on each side of the fork. The stock pieces are made of a rubber. These bushings are made from lightweight billet aluminum.
These AP Engineering billet bushings stabilize the shifter and offer a more precise feel. The stock rubber bushings have some play in them and these billet bushings completely eliminate that.
Over time your stock bushings deteriate into nothing. You can not buy just the stock rubber bushing replacements, you have to buy the whole fork. Even if you did that, you would still have nothing better than the stock bushings.
The kit includes everything pictured here and installation instructions. You need nothing more than a vise to do it yourself. All you have to do is unbolt the shifter tower from the transmission and if you need more room, just unbolt the transmission mount. It's worth it to install considering the stock rubber bushings could never meet the demands of a modified racer.