These plastic inserts allow you to adapt your Mishimoto shift knob to almost any vehicle. Just bought a new project car and you want to start the build off with the shift knob from your daily driver No problem, just find the right adapter, screw it into your shift knob, and install on your shifter. First mod done.This kit includes four adapters to fit multiple vehicles with the following shifter threads M8x1.25, M10x1.5, M10x1.25, and M12x1.25.