Part Type
Aluminum Weld-In Bungs
The right thread and flange to weld into your build.
A weld-in bung is a small turned fitting that you weld into a tank, manifold, header, or chassis to add a threaded port: female NPT, AN, SAE ORB, or a metric sensor thread like the M18x1.5 wideband O2 bung. The bung gets turned to your thread, bore, and flange spec and inspected to gauge; you weld it into your own build, so the fit-up and the weld stay yours. Send a drawing or a sketch with the thread, flange, and material through the quote form and a real person sends back price and lead time in 24-48 hours, with no minimum order.
Updated June 2026
What a weld-in bung is, and matching the metal
A weld-in bung is a small fitting turned from solid that you weld into a tank, manifold, header, chassis tube, or reservoir to add a threaded port where there wasn’t one. The bung is turned to your thread and flange spec; you weld it into your own build. That split matters for fab shops and motorsport: you control fit-up and the weld, the thread and bore are held to print.
The first thing to nail down is material, because a clean weld wants matching metals. Aluminum bung into an aluminum tank, mild steel into a steel header, 304 or 316 stainless into a stainless line. Mixing metals across a weld is how you get cracks and leaks down the road, so the bung material follows whatever you are welding into, not the other way around.
Threads and sizes: NPT, AN, ORB, and sensor bungs
Thread choice is the heart of the part, and most builds pull from a short list. Female NPT in 1/8, 1/4, 3/8, and 1/2 covers oil, coolant, and pressure ports, cut to gauge so a tapered fitting seals. SAE ORB and AN ports in -6, -8, and -10 give you an O-ring seal that doesn’t mind vibration, the usual call for fuel and oil lines on a built engine. When a port needs an adapter instead of a bung, that crosses into custom fittings, and the two get quoted the same way.
Straight AN bungs handle braided line that terminates in a hose end. For sensors, metric is standard: M12x1.5 and M14x1.5 for temp and pressure senders, and the M18x1.5 wideband O2 sensor bung that every standalone tune needs. If your thread isn’t on that list, a custom bore or thread to your drawing is a normal request, not an exception.
Flange styles and profile
Flange style decides how cleanly the bung welds in and how it sits. A flat-bottom (saddle) flange is contoured to wrap a round tube, so it sits flush on a chassis or header instead of bridging the curve. A flat disc flange suits flat tank and reservoir walls. A stepped or recessed flange drops the bung slightly below the surface so you get a clean fillet weld all the way around with no overhang to grind.
Height is the other call: a low-profile bung tucks out of the airstream and clears tight packaging, while a taller bung gives you more thread engagement and keeps the heat of the weld away from a sensor tip. The bore and flange get held to tight tolerances so the fit-up is clean. Tell the team the wall it lands on and the look you want, and the flange gets drawn to match.
Common uses and materials
These show up all over a build. Oil and coolant lines, fuel cells and surge tanks, methanol and nitrous feeds, turbo drains and wastegate plumbing, brake and clutch reservoirs, and temp or pressure sensor ports across the engine. Material tracks the job: 6061 aluminum for tanks and most fuel and oil work, mild steel for headers and exhaust, and 304 or 316 stainless where heat and corrosion both show up.
Every bung gets turned to print and inspected before it ships, threads checked to gauge and bore and flange measured. The bung is made to spec; the weld into your tank or header is yours, and a small weld-in bung kit of mixed threads is an easy way to order. Send a drawing or a sketch with the thread, flange, and material through the quote form and a real person sends back price and lead time in 24-48 hours, with no minimum order.
Questions
Before you send a job.
01 Do you weld the bungs into my tank or header?
No. The bung is turned to your thread, bore, and flange spec and inspected to gauge; you weld it into your own tank, manifold, header, or chassis. That keeps fit-up and the weld in your hands, where a fabricator wants them. The part you get is the finished bung, ready to drop into the hole and weld.
02 What material should a weld-in bung be?
It should match whatever you are welding it into. Aluminum bung for an aluminum tank, mild steel for a steel header, and 304 or 316 stainless for a stainless line. Matching the metal is what gives you a clean, crack-free weld; mixing metals across a weld joint invites leaks down the road, so the bung follows the host part.
03 Which threads can you cut: NPT, AN, ORB, sensor?
All of them. Female NPT in 1/8, 1/4, 3/8, and 1/2 cut to gauge, SAE ORB and straight AN in -6, -8, and -10, and metric sensor threads including M12x1.5, M14x1.5, and the M18x1.5 wideband O2 bung. If the thread you need isn’t on that list, a custom bore or thread to your drawing is a normal request.
04 What flange style should I ask for?
It depends on the surface. A flat-bottom (saddle) flange is contoured to sit flush on a round tube or header, a flat disc flange suits flat tank and reservoir walls, and a stepped or recessed flange lets you run a clean fillet weld with no overhang to grind. Tell the team the wall it lands on and whether you want low-profile or tall, and it gets drawn to match.
05 Can I order one bung, or a mixed kit?
Either. There is no minimum, so a single O2 sensor bung for one build is a normal order, and so is a small weld-in bung kit of mixed NPT, AN, and sensor threads. Per-piece pricing drops as quantity rises since setup spreads across the batch, so the quote can show both a one-off and a small-batch number.
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