The PTRI adjustable seat sliders are designed to be used in conjunction with Tillett seat brackets. They also fit directly to the bottom of the W2, W3 and W4 seats when fitted with the optional backframe which has mounting holes on the bottom. For the standard B6 seat (not Screamer) and the W1i with backframe, the PTRI requires use of the the TK5 spacer kit to mount to the bottom. They have a hole to hole spacing of 31.5cm which is the same as the majority of Tillett's seat brackets. This slider is intended for road car use and should not be used on any track cars.