PD Series couplings provide easy connection for mechanical gauges or specialized diagnostic equipment like SensoControl ®. Typically, PD or BPD nipples are permanently mounted in the system at threaded test ports, in rigid tubing or in hose assemblies. PD couplers are attached to test instruments. Couplers align to the mating nipples without threading. This allows gauges, transducers and other test equipment to be snapped into place without difficulty. Note: Protective dust caps play a crucial role in the life of a quick coupling and no purchase is complete without the selection of an appropriate dust cap.