New, old stock. PARKER BST-6M Quick Connect,Socket,3/4",3/4"-14 Hydraulic Quick Connect Hose Coupling, Socket, ST Series, Brass, Coupling Size 3/4 in, Male, Max. Working Pressure @ 70 F 1,700 psi, Max. Flow Rate 106 lpm ST Series hydraulic quick-connect coupling bodies are the female end of coupling sets. Also called sockets, they accept coupling plugs (nipple or male ends) for use in hydraulics and fluid transfer.ST Series hydraulic quick-connect couplings are valve free to provide maximum air flow with minimal pressure loss. The smooth, open bore allows cleaning in applications where the same lines are used for more than one media including high-pressure water, steam washers, and carpet cleaners. ST Series couplings are interchangeable with similar straight-through high-flow couplings. Steel nipples are case hardened for dent resistance.