External unions have male threads, requiring a nut with female threads. Standard material is 300 series stainless. Also available in Hastelloy C and gold-plated stainless versions.

Select the union with the bore that matches the ID of the tubing. If the IDs are different, choose the union with a bore which matches the smaller tube bore. (A through-type union is illustrated at right.)

Bulkhead versions are designed to be mounted through an instrument panel or on a bracket. The fitting body is undercut so that it bites into the panel when the mounting nut is tightened, eliminating the need for a lock washer.

Note: Because 1/16" external fittings have very thin, easily distorted walls, they are not as durable as 1/16" internal fittings. We recommend the use of external/internal unions when connecting to an installed external nut.