Looking up the across-flats, length and turns of thread for a coupling nut before you draw it, buy a spanner or check a quote? The chart below covers M2 to M24 with DIN 6334 values where the standard exists, ISO 4032 flats where it does not, the turns of thread in the standard length, and the weight per millimetre in 304. No drawing needed: a photo with a rule, the measurements in a message, the old part or its part number is enough; we draw it, you approve, we machine. Get a quote →
Metric coupling nut size chart, M2 to M24
EKINSUN LTD is a custom parts manufacturer that cuts coupling nuts from hex bar to the thread, length and across-flats you specify, from one piece. DIN 6334 gives hex coupling nuts a length of three diameters and the DIN 934 nut across-flats; it starts at M5. M2, M2.5, M3 and M4 have no coupling-nut standard, so the chart shows the ISO 4032 nut flats for them and leaves the length to the order.
| Thread | Coarse pitch | Across flats | Standard length (DIN 6334) | Turns in standard length | Weight, 304 | Lengths we cut |
|---|---|---|---|---|---|---|
| M2 | 0.4 mm | 4 mm | no standard | length ÷ pitch | 0.09 g/mm | 10–100 mm |
| M2.5 | 0.45 mm | 5 mm | no standard | length ÷ pitch | 0.15 g/mm | 10–100 mm |
| M3 | 0.5 mm | 5.5 mm | no standard | length ÷ pitch | 0.17 g/mm | 10–100 mm |
| M4 | 0.7 mm | 7 mm | no standard | length ÷ pitch | 0.27 g/mm | 10–100 mm |
| M5 | 0.8 mm | 8 mm | 15 mm | 19 | 0.33 g/mm | 10–100 mm |
| M6 | 1 mm | 10 mm | 18 mm | 18 | 0.54 g/mm | 10–100 mm |
| M8 | 1.25 mm | 13 mm | 24 mm | 19 | 0.89 g/mm | 10–100 mm |
| M10 | 1.5 mm | 17 mm | 30 mm | 20 | 1.55 g/mm | 10–100 mm |
| M12 | 1.75 mm | 19 mm | 36 mm | 21 | 1.84 g/mm | 10–100 mm |
| M14 | 2 mm | 22 mm | 42 mm | 21 | 2.45 g/mm | 10–100 mm |
| M16 | 2 mm | 24 mm | 48 mm | 24 | 2.76 g/mm | 10–100 mm |
| M18 | 2.5 mm | 27 mm | 54 mm | 22 | 3.55 g/mm | 10–100 mm |
| M20 | 2.5 mm | 30 mm | 60 mm | 24 | 4.32 g/mm | 10–100 mm |
| M22 | 2.5 mm | 32 mm | 66 mm | 26 | 4.71 g/mm | 10–100 mm |
| M24 | 3 mm | 36 mm | 72 mm | 24 | 6.22 g/mm | 10–100 mm |
Inch coupling nut sizes, 4-40 to 3/4-10
Inch coupling nuts follow the ASME B18.2.2 hex nut across-flats but have no length standard; each maker sets its own. The lengths below are the common catalogue values, and the turns column uses them.
| Thread | Major diameter | Across flats (ASME B18.2.2) | Common catalogue length | Turns in that length |
|---|---|---|---|---|
| 4-40 | 0.112 in / 2.85 mm | 1/4 in / 6.35 mm | 1/2 in / 12.7 mm | 20 |
| 6-32 | 0.138 in / 3.51 mm | 5/16 in / 7.94 mm | 1/2 in / 12.7 mm | 16 |
| 8-32 | 0.164 in / 4.17 mm | 11/32 in / 8.73 mm | 1/2 in / 12.7 mm | 16 |
| 10-24 | 0.190 in / 4.83 mm | 3/8 in / 9.53 mm | 3/4 in / 19.1 mm | 18 |
| 1/4-20 | 0.250 in / 6.35 mm | 7/16 in / 11.11 mm | 3/4 in / 19.1 mm | 15 |
| 5/16-18 | 0.3125 in / 7.94 mm | 1/2 in / 12.70 mm | 1 in / 25.4 mm | 18 |
| 3/8-16 | 0.375 in / 9.53 mm | 9/16 in / 14.29 mm | 1-1/8 in / 28.6 mm | 18 |
| 1/2-13 | 0.500 in / 12.70 mm | 3/4 in / 19.05 mm | 1-3/4 in / 44.5 mm | 23 |
| 5/8-11 | 0.625 in / 15.88 mm | 15/16 in / 23.81 mm | 2-1/8 in / 54.0 mm | 23 |
| 3/4-10 | 0.750 in / 19.05 mm | 1-1/8 in / 28.58 mm | 2-1/4 in / 57.2 mm | 23 |
How to read a coupling nut callout
A callout carries four numbers and a material: M10 × 1.5 × 60 × 17 A/F, 304. The first is the thread, the second the pitch, the third the overall length, the fourth the across-flats. Catalogue listings often drop the pitch and the flats, which is where the two most common mistakes come from: a fine-pitch rod meeting a coarse nut, and a spanner that does not fit. Ten threads on the rod measure ten times the pitch; a caliper across the flats gives the spanner size.
Length, turns and where the rod ends
A coupling nut joining two rods gives each rod half its length. In a DIN 6334 nut that is one and a half diameters per rod, about ten to twelve turns, which is more than a standard nut holds. Where a longer nut is ordered, the extra length is usually there to make up distance, not strength; the joining page gives the strength numbers. A sight hole at mid-length shows whether both rods have reached the middle.
Price, lead time, delivery for a nut off this chart
There is no list price for a machined coupling nut; a single piece starts from €65 and is quoted within 12 hours from the callout. One to a few dozen pieces ship in 5 working days, 50 to 500 in 15 working days, delivered DDP to your door with duties in the quote. The first piece is the sample; repeat orders run to the same drawing, and 500-piece and 1,000-piece runs are priced lower per piece. Bar is 304 (1.4301) unless the order says 316 (1.4404), 303 (1.4305), brass CW614N, zinc-plated steel or aluminium 6061; the grade goes on the drawing and the certificate.
Where the chart stops
| What you need | In the catalogue? | What to do |
|---|---|---|
| DIN 6334 sizes M5–M20 in A2 or zinc steel | Yes | Buy it there, or ask us — we may have it in stock |
| M2–M4 as a true coupling nut | No | Cut to order with ISO 4032 flats |
| M22, M24 in stainless | Rare | Cut to order from 32 or 36 mm bar |
| A length that is not three diameters | No | Cut to order, 10 to 100 mm |
| Fine pitch: M10×1.25, M12×1.5, M16×1.5 | Rare | Cut to order; state the pitch |
| Across-flats different from the chart | No | Cut to your spanner |
| Inch coupling nut in a non-catalogue length | No | Cut to order; no standard governs inch lengths |
Related coupling nut pages
Frequently asked
What size is a coupling nut for M10?
17 mm across flats and 30 mm long to DIN 6334, with a 1.5 mm pitch, which gives 20 turns of thread in the standard length. Some suppliers list M10 at 16 mm across flats to the ISO 4032 nut size; check the flats before buying a spanner.
How long is a standard coupling nut?
Three times the thread diameter: M6 is 18 mm, M8 24, M10 30, M12 36, M16 48, M20 60, M24 72 mm. Inch coupling nuts have no single standard; lengths of 1-1/8 in for 3/8-16 and 1-3/4 in for 1/2-13 are common but vary by maker. Any other length is machined.
Is there a coupling nut size chart for M2, M3 and M4?
No standard covers them. This chart uses the ISO 4032 nut across-flats, 4, 5, 5.5 and 7 mm, and lists the length as whatever is ordered, because those sizes are made as standoffs or cut to order rather than stocked as coupling nuts.
How many turns of thread are in a coupling nut?
Length divided by pitch. A DIN 6334 nut always holds about 24 turns at coarse pitch because length and pitch both scale with the diameter: 30 ÷ 1.5 = 20 turns for M10, 72 ÷ 3 = 24 for M24. A 60 mm M10 nut holds 40.
How much does a stainless coupling nut weigh?
The chart gives grams per millimetre of length for a 304 hex body with the thread bored through; multiply by the length. An M10 nut at 30 mm is about 46 g, at 60 mm about 92 g. Use it for shipping and for checking a quote by the kilogram.
Can I get a coupling nut in a size that is not on this chart?
Yes. The chart is the shelf; anything between the rows, above M24, at a fine pitch, or at a different across-flats is cut to order from one piece. Send the callout and the drawing comes back with the quote in 12 hours.
A size between the rows? Send thread, length, flats and material; the drawing and quote come back in 12 hours, MOQ 1. Get a quote →