The function of this shift boot adapter is to take up the space between the bottom of any aftermarket shift knob and your OEM shift boot making your cockpit look clean and complete again. With this shift boot adapter, you will be able to install any AFTERMARKET shift knob without having to worry about any gapping. Now you can buy any aftermarket shift knob of your choice and say goodbye to your ugly OEM shift knob. The shift boot adapter is meant to be used on MANUAL TRANSMISSIONS (ONLY).