The 10023C400 Buttweld End Cap Fitting has 4.0 inch outside diameter and 0.065 in. wall thickness. End caps are used to terminate vacuum tubing in vacuum piping applications. Series 23 vacuum buttweld fittings are constructed with welded, drawn, and annealed 304 stainless steel tubing for applications where minimizing the number of sealed joints is critical. Stainless steel vacuum tubing offers low outgassing under vacuum conditions, is chemically resistant, annealed for consistent leak free welding, and has minimized corrosion concentration points. Series 23 fittings are designed for internal socket type welding or external buttwelding.