DIN 546 Slotted Round Nut
DIN 546 is the simplest of the round nuts: a plain cylindrical body with a single screwdriver slot across the face. No spanner flats, no pin holes, no special tool. It covers an unusually wide size range for a nut standard — M1 to M20 — which makes it the default choice for miniature threaded assemblies. We machine the whole range in brass CW614N and CW617N, including the sub-millimetre slot widths at the small end. Also available in MS and SS 303/304/316 on request.
The size range is the point
Most nut standards start at M3 or M4. DIN 546 goes down to M1, with defined dimensions at M1, M1.2, M1.4, M1.6, M2 and M2.5 before reaching the sizes other standards cover.
That matters because miniature assemblies — instruments, optics, medical devices, electronics, model engineering — need a nut that can actually be driven. A hexagon nut at M1.6 has 3.2 mm flats, which is beyond the practical reach of any spanner in a confined space. A slotted round nut of the same thread has a 0.6 mm slot that a jeweller’s screwdriver engages easily, in a body that seats flush.
Free-cutting brass is well suited to this end of the range. It machines cleanly at small diameters where steel work-hardens and tears, and the slot edges come out sharp rather than burred — which matters when the slot is under a millimetre wide.
DIN 546 dimensions (mm)
| Thread d | Pitch P (mm) | Outside dia. dk (mm) | Height m (mm) | Slot width n nom. (mm) | Slot depth t min (mm) | Slot depth t max (mm) |
|---|---|---|---|---|---|---|
| M1 | 0.25 | 2.50 | 1.00 | 0.3 | 0.3 | 0.5 |
| M1.2 | 0.25 | 3.00 | 1.20 | 0.4 | 0.4 | 0.6 |
| M1.4 | 0.3 | 3.00 | 1.40 | 0.5 | 0.5 | 0.7 |
| M1.6 | 0.35 | 3.50 | 1.60 | 0.6 | 0.6 | 0.8 |
| M2 | 0.4 | 4.50 | 2.00 | 0.8 | 0.8 | 1.0 |
| M2.5 | 0.45 | 5.50 | 2.20 | 0.9 | 0.9 | 1.1 |
| M3 | 0.5 | 6.00 | 2.50 | 1.0 | 1.0 | 1.2 |
| M3.5 | 0.6 | 7.00 | 3.00 | 1.0 | 1.0 | 1.4 |
| M4 | 0.7 | 8.00 | 3.50 | 1.2 | 1.2 | 1.6 |
| M5 | 0.8 | 9.00 | 4.20 | 2.0 | 1.5 | 1.9 |
| M6 | 1.0 | 11.00 | 5.00 | 2.5 | 2.0 | 2.4 |
| M8 | 1.25 | 14.00 | 6.50 | 3.0 | 2.5 | 3.0 |
| M10 | 1.5 | 18.00 | 8.00 | 3.5 | 3.2 | 3.7 |
| M12 | 1.75 | 21.00 | 10.00 | 4.0 | 3.8 | 4.3 |
| M14 | 2.0 | 24.00 | 11.00 | 4.0 | 3.8 | 4.3 |
| M16 | 2.0 | 26.00 | 12.00 | 4.0 | 3.8 | 4.3 |
| M18 | 2.5 | 29.00 | 13.00 | 4.0 | 4.8 | 5.5 |
| M20 | 2.5 | 32.00 | 14.00 | 5.0 | 4.8 | 5.5 |
Values in mm per DIN 546. dk and m shown as nominal (= max); minima are 0.2–0.6 mm lower depending on size. Slot width n is nominal — the standard also defines min and max limits. Confirm against the current standard before release to production.
What the slot can and cannot do
A screwdriver in a slot is a low-torque drive. The blade contacts a narrow band on each side of the slot, and the reaction tries to lift the blade out. In brass, over-torquing does not usually snap the driver — it deforms the slot edges, after which the nut is very difficult to remove.
Design accordingly. DIN 546 belongs on retaining, locating and adjustment duties: holding a spacer stack, retaining a bearing race that is not axially loaded, setting the position of a shaft component, closing off a threaded post. It does not belong on a joint that needs preload.
If you find yourself specifying DIN 546 and then worrying about torque, that is the signal to move to DIN 547 (two-hole face spanner) or DIN 1804 (hook spanner). The three exist as a torque ladder.
Why the outside stays plain
The cylindrical outer surface is the second reason to choose this family. It can be recessed into a counterbore and finish flush; it can rotate against an adjacent component without a hex corner catching; it presents no snag point on an exposed assembly; and it takes a clean knurl if the customer wants finger adjustment added as a modification.
We machine these from bar, so a modified outside diameter, a knurled band or a non-standard height is a straightforward change on a made-to-order run rather than a special tool.
Materials
| Material | Designation | Nominal composition | Note for slotted round nuts |
|---|---|---|---|
| Free-cutting brass | CW614N (CuZn39Pb3) | Cu 57–59%, Pb 2.5–3.5%, Zn balance | Preferred, especially M1–M3 — clean slot edges, no burr |
| Forging brass | CW617N (CuZn40Pb2) | Cu 57–59%, Pb 1.6–2.5%, Zn balance | M8 and above |
| Indian free-cutting brass | IS 319 | Cu 57–59%, Pb 2.5–3.5%, Zn balance | Bulk export runs |
| Other metals | MS, SS 303/304/316 | — | Available on request |
Finishes
Natural mill finish · Nickel plated · Tin plated · Black nickel for optical and instrument work where reflection must be suppressed · Chrome plated. On the smallest sizes, plating thickness is a real consideration — at M1 to M2 a heavy plate measurably changes thread fit, so specify the finish and the thread class together.
Manufacturing capability
Custom manufacturing from drawing or sample · Tolerance ±0.01 mm · MOQ: 500 pcs (typical) · Lead time: 1–2 weeks · ISO 9001:2015 · Export packing · FOB Mundra / CIF worldwide · Brass specialist in Jamnagar, India’s brass city
18+ years of manufacturing experience · 19 skilled workers · Sales@definitemetal.com
Applications & industries
Miniature and precision assemblies at M1–M3 — instruments, optics, medical devices, hearing aids, model engineering · Electronics and PCB hardware · Spacer and standoff stacks · Bearing and bush retention where axial load is light · Adjustment and locating duties on shafts · Any flush or recessed position where a hexagon nut cannot be driven.
Frequently Asked Questions
Down to M1, with defined sizes at M1, M1.2, M1.4, M1.6, M2 and M2.5 before the range reaches sizes shared with other standards. That is the main practical reason to choose this standard — most nut standards begin at M3 or M4, leaving miniature assemblies without a driveable option. The M1 nut has a 2.5 mm outside diameter and a 0.3 mm slot.
Not much, and less in brass than in steel. The blade bears on a narrow band each side of the slot and the reaction lifts the driver out. Over-torquing deforms the slot edges rather than breaking anything, after which removal becomes difficult. Use DIN 546 for retaining, locating and adjustment — not for preloaded joints. Step up to DIN 547 or DIN 1804 if torque is a requirement.
One whose blade matches the slot width and fills as much of the slot length as possible. At the small end this means proper jeweller’s drivers rather than a general-purpose set — a 0.6 mm slot at M1.6 needs a blade ground for it. A blade that is too thin concentrates load on the slot edge and rounds it out on the first use.
They are one family with different drive features and proportions. DIN 546 has a screwdriver slot; DIN 547 has two blind holes in the face for a pin spanner; DIN 548 is a related round nut in the same series. Outside diameters and heights are shared across much of the range, so the choice is about how much torque you need and what tool you have.
No direct ISO replacement. The DIN 546/547/548 round nut family never transferred to an ISO standard, so these DIN references remain the working international reference for the type.
Yes. These are machined from bar, so a knurled band for finger adjustment, a modified outside diameter or a non-standard height are straightforward changes on a made-to-order run — no special tooling required. Send a sketch with your enquiry. MOQ stays at 500 pieces per variant. —