This spacer fits on the Layshaft of 4-speed Hewland and Webster Mk-series and Formula Mazda gearboxes (except Mk5). When used with a narrow 5-Speed Reverse Driver Gear (Part No. 1410-A59H-5, sold separately), this spacer makes up the gap left by removing 1st gear from the 5-speed stack. Hewland part number HC9-238-1.
Some builders simply leave an old 1st layshaft gear in place on the stack, but this low-profile spacer saves weight and rotating inertia.