These adapters convert a 1/4" OD tube made of glass metal or plastic, to a 3/8" OD tube stub for connection to a compression fitting or for welding.

Fitting specifications are shown in the second image.

A "bored through" designation (BT at the end of a Swagelok tube stub adapter fitting part number) indicates the ID of the tube stub as compared to the OD. A bored through fitting allows a tube of the indicated size to fit through the fitting.

Swagelok Ultra-Torr fittings are designed for vacuum system use only and offer reliable vacuum sealing performance up to ultra-high vacuum, even after repeated connects and disconnects. They are constructed of 316 stainless steel and use a knurled nut for easy, finger-tight assembly. No tools are required to assemble or disassemble ultra-torr fittings.

Unlike standard Swagelok compression fittings (used for both vacuum and pressure applications), Ultra-Torr fittings do not use a permanently swaged ferrule on the end of a tube. Instead, the seal is made by compressing an O-ring on the tube end. Because a ferrule is not used, these fittings can repeatedly seal glass, metal or plastic tubing without permanent alteration to the tubing. They are constructed of 316 stainless steel and use a knurled nut for easy, finger-tight assembly. No tools are required to assemble or disassemble ultra-torr fittings.