Part Type
Custom Weld-In Bungs
Weld-in bungs are turned fittings you weld into a tank, header, tube or plate to add a threaded port or mount: a female NPT or ORB port, a male AN flare, an O2 sensor port or a tapped boss. Send the thread, material and base style on a drawing or sketch through the quote form, and a person quotes it in 24-48 hours, with no minimum order. A bung ordered on its own ships loose, the way fabrication and welding shops buy machined details and do their own welding.
Updated September 2026
Example part, modeled for illustration.
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The right thread and base to weld into your build.
Which thread and seal should the bung have?
The thread callout decides how the port seals, so name the seal as well as the size. A bung is a CNC turned part; the table covers NPT, ORB, AN and O2 sensor ports, and any other thread is quoted from your print.
When the port takes an adapter rather than a hose end, the adapter is a custom fitting, and the bung and the fitting can go on one quote. Not every bung is a port: a blind tapped stand-off bung, catalogued in sizes such as M6, M8 and M10, gives a bracket or cover a threaded mount on an aluminum tank or tube (source 6).
| Port | How it seals | Write it as |
|---|---|---|
| Female NPT | Tapered thread, 1 in of diameter per 16 in of length; the flanks seal as the fitting is torqued, with tape or paste on the thread. NPTF (Dryseal) is made to seal without tape or compound. | 1/4-18 NPT, or 1/4-18 NPTF |
| Female ORB port (SAE J1926-1) | Straight UNF thread holds the fitting; the O-ring on the fitting seals in a chamfer at the top of the port, not on the thread. O-rings are not supplied. | -8 ORB port (SAE J1926-1), 3/4-16 UNF-2B |
| Male AN flare | 37 degree flared end, metal to metal; a female AN hose end or tube nut threads onto it. | -6 AN male, 9/16-18 |
| O2 sensor port | Straight M18x1.5 thread, the size Bosch gives for its LSU 4.9 wideband sensor; the sensor seats on the top face of the bung. | M18x1.5 |
How big does the face of the bung need to be?
An ORB port needs a flat face around it. Parker’s SAE J1926-1 port table gives a recommended spotface diameter of 25 mm on a -6, 30 mm on a -8 and 34 mm on a -10; where the boss face is a machined surface, its footnote says that diameter need not apply as long as the R0.2 corner radius at the port is kept (source 3). Give the face diameter on the print.
For a wideband O2 bung, the Bosch LSU 4.9 data sheet draws a recommended boss: M18x1.5, 25 mm across and a minimum length of 10.5 mm, or 13 mm where the sensor hex runs above 600°C or the gas above 930°C, with flatness and finish callouts on the face the sensor seats on (source 5). Copy those onto the bung print.
What metal should a weld-in bung be?
Order the bung in a metal that welds to the part it goes into. Steel and aluminum are rarely if ever fusion welded to each other with TIG or MIG, because brittle intermetallic compounds form in the weld (source 7), so an aluminum tank takes an aluminum bung and a steel pipe takes a steel or stainless one. A 6061 aluminum bung is typically welded with 4043 or 5356 filler (source 8).
A stainless bung on a mild steel pipe is a dissimilar joint with its own filler: Hobart lists its 309/309L wire for joining 300-series stainless to carbon steel (source 9). A bung welded into stainless can be drawn in 304L, which holds carbon to 0.035% maximum so the weld does not sensitize the metal beside it (source 10); stainless steel parts covers the grades. Other alloys and plastics quoted on request. Name the grade on the print.
Flat, radiused or stepped: which base does the bung need?
A flat base suits a flat wall: a tank side, a plate, a reservoir. On a round tube, a radiused base is cut to the tube’s outside diameter so the bung sits down on the curve and welds more cleanly to the tube (source 11). A stepped bung carries a short lip below the base that centers it in the drilled hole and keeps it aligned while it is welded (source 12).
Height is the other number. A taller body, or an extended shoulder, puts more metal between the weld and the thread and limits thread distortion during welding (source 12).
What should I send for a bung quote?
Beyond the thread callout and the material grade, the print needs the base style with the tube OD for a radiused base or the hole size for a stepped one, the overall height, the base diameter and any bore through the bung. With a STEP model and no drawing, the bung is quoted to a ±0.005 in general tolerance, or the one your notes name, as STEP-only quoting explains.
A fully dimensioned 2D PDF is quoted without a CAD line. A new sample bung can start the quote as well as a sketch; if a model has to be drawn from either, the CAD is quoted as its own line. The flanges and fittings that can go on the same order are listed under custom machined parts.
Sources
All accessed 27 September 2026. Where a figure here differs from your print, the print governs.
1. Wikipedia, "National pipe thread": en.wikipedia.org/wiki/National_pipe_thread (ASME B1.20.1; taper of 1 in of diameter in 16 in of length; the flanks compress to seal when torqued; lubricated with paste or tape; NPTF seals without tape or compound).
2. Wikipedia, "O-ring boss seal": en.wikipedia.org/wiki/O-ring_boss_seal (the seal is an O-ring in a chamfered area, not the thread).
3. Parker Hannifin, "4300 Catalog, Table U18: Port Detail, SAE J1926-1 (ISO 11926-1)", page U26, hosted by Goodyear Rubber Products, goodyearrubberproducts.com/files/parker/parkertubecatalog4300/parker%20tube%20catalog%204300examin1.page477.pdf (straight UN/UNF O-ring port; -6 9/16-18, -8 3/4-16 and -10 7/8-14 UNF-2B; recommended spotface diameters 25, 30 and 34 mm; footnote 3, machined boss face; the same figures appear as Table S23 in Catalog 4300 PDF version 11, June 2025).
4. Wikipedia, "AN thread": en.wikipedia.org/wiki/AN_thread (37 degree flare, metal-to-metal seal; dash number is the tube OD in sixteenths of an inch; -6 is 3/8 in tube with a 9/16-18 thread).
5. Bosch Motorsport, "Lambda Sensor LSU 4.9" data sheet, 27 January 2026: bosch-motorsport.com/content/downloads/Raceparts/Resources/pdf/Data%20Sheet_69034379_Lambda_Sensor_LSU_4.9.pdf (M18x1.5 thread; hexagon temperature under 600°C; recommended design of the mating thread; installation notes).
6. Vibrant Performance, "Stand Off Weld Bung": vibrantperformance.com/stand-off-weld-bung/ (6061 aluminum; M6, M8 and M10; mounting components to aluminum structures).
7. Denzel Bridges, "Steel-Aluminum Welding: Issues and Work-Arounds", Red-D-Arc, 16 August 2022: blog.red-d-arc.com/steel-aluminum-welding-issues-and-work-arounds/ (steel and aluminum are rarely, if ever, directly fusion welded, because of brittle intermetallic compounds).
8. Wikipedia, "6061 aluminium alloy": en.wikipedia.org/wiki/6061_aluminium_alloy (typical filler material 4043 or 5356).
9. Hobart Brothers, "309/309L" filler metal data sheet, revision 160923: hobartbrothers.com/wp-content/uploads/hobart-catalog/datasheets/309_309L.pdf (for joining 300-series stainless steels to carbon or low alloy steels).
10. Wikipedia, "SAE 304 stainless steel": en.wikipedia.org/wiki/SAE_304_stainless_steel (304L carbon 0.035% maximum; low carbon prevents sensitization during welding).
11. Vibrant Performance, "Saddle Style O2 Sensor Weld Bungs": vibrantperformance.com/saddle-style-o2-sensor-weld-bungs-v1015/ (304 stainless; a radius design for a cleaner weld to tubing).
12. Ticon Industries, "Aluminum AN ORB Weld Bung": ticonindustries.com/products/aluminum-an-orb-weld-bung (bottom lip for alignment and centering during welding; extended shoulder to minimize thread distortion).
13. Pegasus Auto Racing Supplies, "Female Aluminum AN Weld Bung (O-ring Port)": pegasusautoracing.com/productselection.asp?Product=3228-126 (a female AN port sealed with an O-ring; -6 9/16-18, -8 3/4-16).
14. AEM, "Installation Instructions for 30-4110NS Gauge-Type UEGO Controller", rev. 151130, 2015: documents.aemelectronics.com/techlibrary_30-4110ns_digital_wideband_uego_gauge_no_sensor.pdf (weld-in M18x1.5 boss; 18 in and 36 in downstream; after the turbo, before the catalytic converter; at least 10 degrees from horizontal, connector up).
Questions
Before you send a job.
01 Do you weld the bungs into my tank or header?
Not into your own tank or header; that weld is yours. Welding is quoted when a job calls for it: a bung welded into a machined part, or into a laser-cut plate, tab or bracket, made to your print in the same order is quoted with the weld included, and laser cut and welded parts covers what a welded print needs. The flat parts around a bung on an off-road build are on laser-cut automotive and off-road parts.
02 Is a -6 AN bung the same as a -6 ORB bung?
Same thread, different seal. The dash number is the tube OD in sixteenths of an inch, so -6 is 3/8 in, and a -6 male AN flare and a -6 ORB port both use a 9/16-18 thread (sources 3 and 4). Racing catalogs also sell “female AN” weld bungs that are O-ring ports (source 13), so write “male AN flare” or “ORB port, SAE J1926-1” rather than “-6 AN” alone.
03 Where should a wideband O2 sensor bung go?
Where the sensor maker says. Install instructions for a wideband gauge that runs the Bosch LSU 4.9 put the bung at least 18 in downstream of the exhaust port, or 36 in or more with a turbo, exhaust gas over 800°C, long high-rpm running or leaded fuel; after the turbocharger; ahead of any catalytic converter; and tilted at least 10 degrees from horizontal with the connector up, so liquid cannot collect at the sensor element on a cold start (source 14). Bosch adds: not near the pipe outlet, where outside air can reach the sensor (source 5).
04 Can I order one bung, or a mixed set?
Either. One O2 bung for one build is a normal order, and a mixed set, such as two -8 ORB ports, a 1/4 NPT and an M18x1.5, goes on one quote. Ask for more than one quantity, such as 1, 25 and 100, and the quote shows each. A bung you reorder can also be quoted as a blanket order and delivered in releases. Price, release schedule and lead time per release are set in the quote.
05 How fast can a bung ship?
Rush 1-2 weeks applies to machined parts with no secondary operations. Heat treat, grinding, EDM and finishing add time, and the quote gives the real date. Lead time starts at order approval. Put your need date in the part description and the quote answers it.
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