ARB RD74 - Manual (Page 13)

3 Installing the Air Locker
11
3.3 Drilling and Tapping the Bulkhead Port
An air line port must be drilled and tapped through the differential
housing to mount the bulkhead fitting into.
Mark a spot on the right hand side (opposite the ring gear) toward
the top of the differential housing that is in an area well clear of the
differential, the ring gear, and any other obstructions that could
snag the seal housing tube. (Fig.6.)
Figure 6.
Cover the drive pinion area with a rag to protect it from metal filings.
Secure the differential housing to the work bench.
Drill an 11.2mm [7/16”] diameter hole through the differential
housing square to the outside surface. (Fig.7.)
Figure 7.