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Hex Weld Nut with Flange Dimensions (ISO 21670, M5 to M16)

Guide · Updated October 28, 2026

ISO 21670 covers hexagon weld nuts with flange, product grade A, sizes M5 to M16 coarse and fine pitch. Values come from the ISO 21670:2014 preview table and agree with the 164580.com ISO 21670 table on every value shown. The Fasenco and Fixingz tables agree on hex, flange diameter, height and flange thickness (Fixingz labels height as K). Not shown: the plate thickness and hole diameter table and the projection details, which we could only confirm from the ISO preview. Check the current edition or your supplier for critical work.

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Step by step

Confirm the size: ISO 21670 covers M5 to M16 coarse, plus fine pitch M8 x 1 to M16 x 1.5, product grade A.
Read the hex: s max is the hex: M6 10 mm, M8 13 mm, M10 16 mm, M12 18 mm.
Check the flange: dc is the round flange that sits on the sheet: M8 22.5 mm max, M10 26.5 mm max. Leave room for it on the part.
Check the height: m is the nut height: M8 10.00 mm max, M10 13.00 mm max.
Mind the flange thickness: b is the flange thickness, about 2.7 to 3.7 mm. The weld projections sit on its underside.
Match the bolt: Rated for bolts up to property class 10.9. Run a tap or clean the thread after welding if spatter gets in.

ISO 21670 hex weld nut with flange dimensions (mm)

Columns: thread size (fine pitch options in brackets), width across flats s max and min, width across corners e min, flange diameter dc max and min, nut height m max and min, flange thickness b max and min.

Size | s max | s min | e min | dc max | dc min | m max | m min | b max | b min
M5 x 0.8 | 8 | 7.64 | 8.2 | 15.5 | 14.5 | 5.00 | 4.70 | 2.20 | 2.00
M6 x 1 | 10 | 9.64 | 10.6 | 18.5 | 17.5 | 7.00 | 6.64 | 2.70 | 2.50
M8 x 1.25 (M8 x 1) | 13 | 12.57 | 13.6 | 22.5 | 21.5 | 10.00 | 9.64 | 2.70 | 2.50
M10 x 1.5 (x 1.25, x 1) | 16 | 15.57 | 16.9 | 26.5 | 25.5 | 13.00 | 12.57 | 2.95 | 2.75
M12 x 1.75 (x 1.5, x 1.25) | 18 | 17.57 | 19.4 | 30.5 | 29.5 | 15.00 | 14.57 | 3.20 | 3.00
M14 x 2 (M14 x 1.5) | 21 | 20.48 | 22.4 | 33.5 | 32.5 | 17.00 | 16.16 | 3.45 | 3.25
M16 x 2 (M16 x 1.5) | 24 | 23.48 | 25.0 | 36.5 | 35.5 | 19.50 | 18.66 | 3.70 | 3.50

Worked example: bolt length into an M8 weld nut

Bracket 3 mm thick bolted to sheet with an M8 weld nut on the back. The bolt must pass the bracket, the sheet (1.5 mm), and engage the nut m min 9.64 mm. 3 + 1.5 + 9.64 = 14.1 mm, so an M8 x 16 bolt fully engages without bottoming on anything behind.

Common problems

Weld spatter in the thread: mask or chase the thread after welding.
Hole too big: the nut can shift or weld off-center; use the supplier hole size.
Coated nuts: zinc or oil can spoil projection welds; use plain nuts unless the process allows.

FAQ

What is an ISO 21670 weld nut?

A hex nut with a round flange whose underside has weld projections. It is resistance welded onto sheet metal to give a strong threaded point.

What wrench fits an M8 ISO 21670 weld nut?

13 mm, but once welded you normally hold the bolt, not the nut.

Does ISO 21670 include fine thread?

Yes: M8 x 1, M10 x 1.25, M10 x 1, M12 x 1.5, M12 x 1.25, M14 x 1.5 and M16 x 1.5. Dimensions match the coarse size.

How is ISO 21670 different from DIN 929?

DIN 929 is a plain hex weld nut with three corner projections and no round flange. ISO 21670 has a full flange that spreads the weld.

What bolt grade can I use?

The standard says bolts up to property class 10.9 per ISO 898-1.

What sheet thickness and hole size?

The standard gives a connecting dimension table for plate thickness and hole; check it or your nut supplier, as we only show values confirmed by multiple sources.

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