Weld-On Fittings

Weld-on fittings add a threaded port, a hose connection or a filler opening to a fabricated part such as a tank, sump or intercooler pipe. All of them are aluminium: NPT and metric threaded bungs, hose barbs, a 50 mm welding neck and a fuel filler neck with cap.

A bung gives a thin wall enough material to carry a thread. The two thread systems seal differently. NPT is tapered and seals on its flanks with a suitable sealant. A parallel metric thread such as M18 × 1.5 seals on a washer or O-ring at its face.

Because aluminium cannot be welded to steel by ordinary means, these fittings are for alloy tanks, pipes and sumps. Pick each one by what will connect to it:

• Threaded bungs: 1/8, 1/4 and 3/8 in NPT, in packs of two, and an M18 × 1.5 bung. Match the thread of the sensor, plug or adaptor that will go in.
• Hose barbs: 6.5, 9.5, 12.5, 15.8 and 19 mm, matched to the inside diameter of the hose. Barbs suit low-pressure lines such as breathers, drains and coolant, with a clamp behind the barb.
• Necks: a 50 mm welding neck, and a large fuel filler neck that needs a 50 mm hole and comes with cap and O-ring. The filler neck can also be fitted to a hose instead of welded.

TIG-weld aluminium with a filler suited to the parent alloy, after cleaning the oxide from both parts. Welding heat can distort a thread, so weld with a spare plug or bolt screwed in, coated with anti-seize, and chase the thread afterwards. Place sensor bungs where the probe sits in the flow, and drain bungs at the lowest point.

Never weld a tank that has held fuel until it has been cleaned and made vapour-free. Leak-test the finished part with low air pressure and soapy water before it goes in the car, and check your class rules on fuel filler and cap design.