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 5920-00-212-4387
NSN 5965-00-614-7280
NSN 6145-01-377-5130
NSN 5999-00-988-0356
NSN 5990-00-576-4882
NSN 6105-00-112-9099
NSN 5996-01-400-3558
NSN 5960-01-437-7422
NSN 6685-01-551-1293
NSN 5835-01-412-0344
NSN 5960-01-045-3566
NSN 6130-00-558-5844