Joining two lengths of threaded rod, or extending one, and unsure how long the coupling nut has to be, whether it is as strong as the rod, or what pitch the rod actually has? The numbers are below, by size, and the nut, the rod and the lock nuts are made here to the same callout. 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 →
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. A coupling nut gives each rod half its length. The table shows what a DIN 6334 nut gives, in millimetres and in turns, and what our longest nut at 100 mm gives, for coarse-pitch rod.
| Rod | Pitch | DIN 6334 nut | Engagement per rod | Longest nut we cut | Engagement per rod |
|---|---|---|---|---|---|
| M6 | 1 mm | 18 mm | 9 mm / 9 turns | 100 mm | 50 mm / 50 turns |
| M8 | 1.25 mm | 24 mm | 12 mm / 10 turns | 100 mm | 50 mm / 40 turns |
| M10 | 1.5 mm | 30 mm | 15 mm / 10 turns | 100 mm | 50 mm / 33 turns |
| M12 | 1.75 mm | 36 mm | 18 mm / 10 turns | 100 mm | 50 mm / 29 turns |
| M14 | 2 mm | 42 mm | 21 mm / 10 turns | 100 mm | 50 mm / 25 turns |
| M16 | 2 mm | 48 mm | 24 mm / 12 turns | 100 mm | 50 mm / 25 turns |
| M18 | 2.5 mm | 54 mm | 27 mm / 11 turns | 100 mm | 50 mm / 20 turns |
| M20 | 2.5 mm | 60 mm | 30 mm / 12 turns | 100 mm | 50 mm / 20 turns |
| M22 | 2.5 mm | 66 mm | 33 mm / 13 turns | 100 mm | 50 mm / 20 turns |
| M24 | 3 mm | 72 mm | 36 mm / 12 turns | 100 mm | 50 mm / 17 turns |
A2-70 stainless threaded rod is rated at 700 MPa tensile. The rod breaks at its stress area long before a coupling nut with one and a half diameters of engagement strips, so the joint is as strong as the rod. The table gives the rod breaking load; the nut only has to be longer than one diameter per rod to reach it.
| Rod | Stress area (ISO 898-1) | A2-70 breaking load, 700 MPa | Coupling nut engagement needed |
|---|---|---|---|
| M6 | 20.1 mm² | 14.1 kN | ≥ 6 mm per rod; DIN 6334 gives 9 |
| M8 | 36.6 mm² | 25.6 kN | ≥ 8 mm per rod; DIN 6334 gives 12 |
| M10 | 58 mm² | 40.6 kN | ≥ 10 mm per rod; DIN 6334 gives 15 |
| M12 | 84.3 mm² | 59.0 kN | ≥ 12 mm per rod; DIN 6334 gives 18 |
| M16 | 157 mm² | 109.9 kN | ≥ 16 mm per rod; DIN 6334 gives 24 |
| M20 | 245 mm² | 171.5 kN | ≥ 20 mm per rod; DIN 6334 gives 30 |
| M24 | 353 mm² | 247.1 kN | ≥ 24 mm per rod; DIN 6334 gives 36 |
Threaded rod is sold in coarse pitch by default, but fine-pitch rod exists at M10 and above and looks identical. Ten threads on the rod measure ten times the pitch: 15 mm for M10×1.5, 12.5 for M10×1.25. A caliper across the crests gives the diameter. Send both numbers, or a photo with a rule, and the nut is cut to match.
| Ten threads measure | Rod | Nut to order |
|---|---|---|
| 10.0 mm | M6×1 or M8×1 fine | M6 coupling nut, or M8×1 fine to order |
| 12.5 mm | M8×1.25 or M10×1.25 fine | M8 coupling nut, or M10×1.25 to order |
| 15.0 mm | M10×1.5 or M12×1.5 fine | M10 coupling nut, or M12×1.5 to order |
| 17.5 mm | M12×1.75 | M12 coupling nut |
| 20.0 mm | M14×2, M16×2 | M14 or M16 coupling nut |
| 25.0 mm | M18×2.5, M20×2.5, M22×2.5 | M18, M20 or M22 coupling nut |
| 30.0 mm | M24×3 | M24 coupling nut |
Under static load, one and a half diameters of thread per rod holds by friction. Under vibration, a hex nut jammed against each face of the coupling nut, or a thread-locking compound on one rod, keeps it from walking. A sight hole at mid-length shows the rods have met; a cross hole gives a bar to tighten against the lock nuts when no spanner reaches.
Where the rod must be a set length overall, or a metric rod meets an inch one, we cut the rod, the coupling nut and the lock nuts together to the same class of thread and test-assemble them. One drawing, one quote, one box.
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.
| What you need | In the catalogue? | What to do |
|---|---|---|
| A2 coupling nut for coarse rod, M6–M20 | Yes | Buy it there, or ask us — we may have it in stock |
| Coupling nut for fine-pitch rod | Rare | Cut to order, state the pitch |
| Coupling nut longer than three diameters for an extension | No | Cut to order, up to 100 mm |
| Metric rod to inch rod in one nut | No | Reducing coupling nut, MOQ 1 |
| Rod and nuts as a matched set | No | Made and test-assembled together |
| Stainless coupling nut with sight hole for inspection | No | Drilled to order |
How long should a coupling nut be to join two threaded rods?
Long enough for each rod to engage at least one diameter, so two diameters minimum and three by DIN 6334, which gives each rod one and a half diameters: about ten turns at M10. That already exceeds a standard nut. Extra length beyond that is for making up distance, adjustment or a sight hole, not for strength.
Is a coupling nut as strong as the rod?
The joint is limited by the rod, not the nut, once engagement exceeds about one diameter per rod. A2-70 threaded rod has a tensile strength of 700 MPa; on the M10 stress area of 58 mm² that is about 40 kN. A 304 coupling nut three diameters long holds that with margin; it is the rod that breaks first.
Can I use a coupling nut to extend a threaded rod?
Yes: rod, coupling nut, rod, with a sight hole to confirm both have reached the middle, and a lock nut against each face if the joint carries vibration. For a rod that must be one length overall, order the rod and nut together and we cut both.
Can you make the same nut but for M10 rod on one end and 3/8-16 on the other?
Yes. A reducing or metric-to-inch coupling nut has each end tapped to its own thread with a short plain bore in the middle; the wall limit is set by the larger thread. The reducing-nut page lists the pairs and the flats that leave enough wall.
Do I need lock nuts with a coupling nut?
Under vibration, yes: a hex nut jammed against each end of the coupling nut, or a thread-locking compound. Under static load the friction of one and a half diameters of thread per rod is enough. A cross-drilled coupling nut lets you tighten it against the lock nuts without flats.
How quickly can you make coupling nuts for a rod job?
Small quantities in 5 working days after the drawing is approved, quoted within 12 hours, delivered DDP. Rod and nuts together take the same time.
Send the rod callout and the overall length. "M12 A2 rod, two pieces joined, 1,200 mm overall, 304 nut with sight hole" is enough. Quote in 12 hours, MOQ 1. Get a quote →
Nut length by size, strength numbers, rod and lock nuts made together. Quote in 12 hours, MOQ 1.
Send a drawing, sketch, sample or photo — reply within 12 hours. MOQ 1.