3. We started our install by gutting the axle, and cleaning out the housing. We used a 7/16-inch (15/32 will also work) drill bit to cut the hole in the top of the differential (make sure to locate an appropriate spot that has clearance for all moving parts in the axlehousing). After the hole is drilled, you’ll need to use a 1/4-inch BSP (British Standard Pipe) tap to create the proper threaded hole for the TJM air bulkhead to install into the housing. Do not use 1/4 NPT! It will not work and you’ll disfigure the bulkhead. TJM is thinking of including these taps with the lockers since BSP tap sizes are not readily available at every hardware store across America. We also took this opportunity to mock up how the actuator’s copper air line fits into the bulkhead.