Weld-On Fittings

Weld-on bungs, flanges, O2 sensor bosses, filler necks and weld-in adapters — parts.

Match the fitting material to the tube you are welding it to. Mild steel to mild steel is straightforward; aluminum bungs need aluminum tube and AC TIG; and stainless wants the correct filler and a back purge if the joint carries exhaust gas. A stainless bung welded to aluminized tube will crack at the joint eventually.

Position matters as much as the weld. An O2 sensor boss should sit at or above the horizontal so condensation cannot pool in the sensor, and it needs enough clearance for the sensor body and its harness. Drain and filler bungs belong at the lowest and highest points respectively — obvious until the part is already welded in.