Double nipples, parallel thread
Threaded fittings
Double nipples with a parallel thread carry a male G thread at both ends, joining two female threaded parts directly, either in equal sizes or as a reduction. The range covers 101 versions, thread sizes from G 1/8" to G 2" plus pressure ratings from PN 16 to PN 40.
A parallel thread does not seal in the thread flanks: sealing is done by a sealing element or a sealing edge on the mating part, such as a flat gasket or a sealing cone inside the valve. This keeps the nipple removable several times over without changing the depth of engagement. Materials are brass/gunmetal, nickel plated brass along with stainless steel 1.4571, the latter covering the versions rated 40 bar.
Take both thread sizes from the two mating parts, then fix the pressure rating. Since the parallel thread seals nothing by itself, the mating part has to provide a sealing face or a seat for a flat gasket; where that seat is missing, the tapered version is the correct choice. The spanner size of 19 to 60 mm defines the open ended wrench needed as well as the free space at the installation point.
Joining ball valves, filter regulators plus manifold blocks in compressed air networks, where two female threaded parts meet without an intermediate piece. In water plus cooling circuits they act as a short adapter between a valve body and a hose tail. Versions in 1.4571 rated PN 40 serve test benches, chemical plants along with process equipment.
