A sealed rear end housing builds internal pressure as the gear oil heats up, and that pressure has to go somewhere, usually past a seal or gasket. This vent threads into the housing or axle tube and lets that pressure equalize, so seals and gaskets stay dry instead of weeping under a hot highway pull.

Strange Engineering H1112B Axle Housing Vent Features:

• Installs in a housing or axle tube
• Equalizes internal pressure during temperature changes
• Helps prevent seal and gasket leaks
• 7/16 in.-20 thread
• 9/16 in. wrench size
• 1.065 in. total height
• Sold individually