Source calls item a union, pipe; can be used as straight adapter external pipe to internal tube
An externally threaded fastening device which has an internal or external seat, designed to mate with the seat of an internally threaded tube fitting for the purpose of securing the tube to the fitting to form a leakproof connection.
NSN 5925-01-469-8104
NSN 6105-01-212-9245
NSN 6685-01-424-0497
NSN 6105-01-528-7557
NSN 5990-01-147-3345
NSN 5950-01-220-0681
NSN 6320-00-242-3300
NSN 6145-00-156-4394
NSN 6240-00-009-8805
NSN 6150-01-502-9532
NSN 2925-00-906-0421
NSN 5915-01-029-4920