Improper installation is the Achilles heel of the ARB Air Locker, and that's why we went to the proven gear installers at One Ton Off-Road. For years we've run ARBs that One Ton has set up, with zero issues. That's important when a functioning locker is all that stands between sleeping in your truck or driving home from a muddy rocky trail. As with every Air Locker, the RD139 requires the housing be drilled and tapped for the air fitting (arrow). The copper tube seen in photo 3 runs through this fitting to the air line.