Hot tub plumbing air fittings are generally small couplings and pipe joiners to connect pipe going to the connections onto the backs of the hot tubs jets.
Barb Adaptor 1/2" Socket or 3/4" Spiggot x 3/4" RibbedBarb
Barb adaptor Tee 1" Socket x 1" Socket x 3/8" RibbedBarb
Pipe joiner reducer 3/8" RibbedBarb x 1/4" RibbedBarb