A hole had been drilled in the top of the housing to provide an exit for the ARB line. It was also tapped 1/4 NPT to accept a supplied brass fitting. Here you can see the copper line being routed through the tapped hole prior to it being cut to final length with a tubing cutter. With the addition of the outside ARB fittings, the differential build was complete and only needed a quick functional check using an air supply. Following the gear manufacturer's break-in suggestions, the differential should be good to go.