A straight bulkhead union in AN10, used to carry a fluid line cleanly through a firewall, boot floor, tank wall or chassis panel. One end carries a longer threaded shank so the fitting can be dropped through a drilled hole and locked in place with a bulkhead nut, leaving a male 37° flare facing each side ready for standard AN hose ends or adapters. AN10 is a common choice for main fuel feed, oil supply and return, and gearbox or engine oil cooler runs. Note that the bulkhead nut and any sealing washer are separate items, and the panel hole must be sized to the shank rather than the flare.