# Square nuts, DIN 557: M5–M20 width across flats, thickness, corner distance + 8 envelope files

> What are the dimensions of a DIN 557 square nut, and how big a slot does an M6 square nut need?

- Category: Hardware › Fasteners
- Kind: Standard part
- Basis: fasten.it's DIN 557 table (M5 to M16, 01/1994) and CDE Fasteners' sheet (M5 to M20); they agree on thickness and corners, and fasten.it prints two variants for M10 and M12; eight envelope files
- Page: https://xemstudio.com/objects/square-nuts-din-557/ · JSON: https://xemstudio.com/api/geometry?object=square-nuts-din-557 · Plain text: https://xemstudio.com/objects/square-nuts-din-557/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files CC BY 4.0 or their publisher's license
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

## Overall (mm)

| length | width | height |
|---|---|---|
| 24.0 | 24.0 | 13.0 |

**Exact dimensions.** Every file is drawn at true size with no tolerance added. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your process's clearance before making the part.

## Notes

- Columns (mm): d thread, P pitch, s width across flats (square side; nominal = max), e max across corners, m nominal thickness (= max), mw min, dw min (the washer-face diameter as printed, all as fasten.it labels them). CDE's columns F, G, H are the width across the square, the width across corners (min) and the thickness.
- Two variants: fasten.it prints two rows each for M10 (s 16 with e 22.6, and s 17 with e 24) and M12 (s 18 / 25.4 and s 19 / 26.9), and does not say why. CDE prints only the larger one (M10 17 / 24, M12 19 / 26.9). The files carry both for M10 and M12 (second variant marked -v2). M5, M6, M8 and M16 agree in both sources; M20 is CDE only (30 / 42.4 / 16).
- Files are Xem-drawn envelopes: a square s × s of thickness m with a plain bore at the thread major diameter. The e value is the printed corner distance of the chamfered nut; the file's square corners are slightly further out (s·√2), as the file note says. Chamfer and thread are not modelled. For a captive-nut pocket of a square nut, the width across flats and the thickness are the numbers needed.
- Nuts for square-head bolts and slide-in T-nuts: slide-in-t-nuts, drop-in-t-nuts. McMaster-Carr's square-nut pages found by search are inch; they are linked, not copied. No metric (DIN 557) McMaster category URL was returned.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| square body | s × s × m: M5 8 × 8 × 4, M6 10 × 10 × 5, M8 13 × 13 × 6.5, M10 16 or 17 × 8, M12 18 or 19 × 10, M16 24 × 24 × 13 mm | square pocket or slot that captures the nut: side = s + your process clearance, depth = m | slide | square-nut-din-557-* |
| bore (thread as plain cylinder) | nominal thread diameter M5 to M16 | bolt of the same thread (plain cylinder at the major Ø) | designed | square-nut-din-557-* |

## Sizes

| thread | P (mm) | s (square side) | e max (across corners) | m (thickness) | mw min | dw min | CDE F / G / H |
|---|---|---|---|---|---|---|---|
| M5 | 0.8 | 8 | 11.3 | 4 | 2.5 | 6.7 | 8 / 11.3 / 4 |
| M6 | 1 | 10 | 14.1 | 5 | 3.2 | 8.7 | 10 / 14.1 / 5 |
| M8 | 1.25 | 13 | 18.4 | 6.5 | 4.1 | 11.5 | 13 / 18.4 / 6.5 |
| M10 | 1.5 | 16 | 22.6 | 8 | 5.2 | 14.5 | — |
| M10 (second variant) | 1.5 | 17 | 24 | 8 | 5.2 | 15.5 | 17 / 24 / 8 |
| M12 | 1.75 | 18 | 25.4 | 10 | 6.6 | 16.5 | — |
| M12 (second variant) | 1.75 | 19 | 26.9 | 10 | 6.6 | 17.2 | 19 / 26.9 / 10 |
| M16 | 2 | 24 | 33.9 | 13 | 8.6 | 22 | 24 / 33.9 / 13 |
| M20 | 2.5 | — | — | — | — | — | 30 / 42.4 / 16 (CDE only) |

## Where the files are

- fasten.it: [DIN 557 square nuts, product grade C (01/1994): d, P, dw min, e max, m, mw min, s, M5 to M16 incl. two variants for M10 and M12](https://fasten.it/en/norms/norm/din_557) — web — Reference page; numbers only
- CDE Fasteners: [DIN 557 square nuts: F width across square, G across corners (min), H thickness, M5 to M20](https://cdefasteners.com/sites/default/files/product-specs/metd557.pdf) — web — Maker data sheet; numbers only
- McMaster-Carr: [Machine screw square nuts (inch) (free STEP/IGES per part, for your own design use; no redistribution)](https://www.mcmaster.com/machine-screw-square-nuts) — STEP, IGES, PDF — McMaster-Carr site terms: personal design use, no redistribution (verify at link)
- McMaster-Carr: [Round-top square nuts (inch) (free STEP/IGES per part, for your own design use; no redistribution)](https://www.mcmaster.com/products/round-top-square-nuts/) — STEP, IGES, PDF — McMaster-Carr site terms: personal design use, no redistribution (verify at link)

## Free STEP/STL (8 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/square-nuts-din-557/index.json

- square-nut-din-557-m5-s-8-m-4: [STEP](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m5-s-8-m-4.step) · [STL](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m5-s-8-m-4.stl) — M5 DIN 557 square nut envelope: 8 × 8 mm square (s), 4 mm thick (m), plain Ø5 bore at the thread major; corners are square, so the corner distance is 11.3 mm against the printed e max 11.3; no chamfer or thread
- square-nut-din-557-m6-s-10-m-5: [STEP](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m6-s-10-m-5.step) · [STL](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m6-s-10-m-5.stl) — M6 DIN 557 square nut envelope: 10 × 10 mm square (s), 5 mm thick (m), plain Ø6 bore at the thread major; corners are square, so the corner distance is 14.1 mm against the printed e max 14.1; no chamfer or thread
- square-nut-din-557-m8-s-13-m-6.5: [STEP](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m8-s-13-m-6.5.step) · [STL](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m8-s-13-m-6.5.stl) — M8 DIN 557 square nut envelope: 13 × 13 mm square (s), 6.5 mm thick (m), plain Ø8 bore at the thread major; corners are square, so the corner distance is 18.4 mm against the printed e max 18.4; no chamfer or thread
- square-nut-din-557-m10-s-16-m-8: [STEP](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m10-s-16-m-8.step) · [STL](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m10-s-16-m-8.stl) — M10 DIN 557 square nut envelope: 16 × 16 mm square (s), 8 mm thick (m), plain Ø10 bore at the thread major; corners are square, so the corner distance is 22.6 mm against the printed e max 22.6; no chamfer or thread
- square-nut-din-557-m10-v2-s-17-m-8: [STEP](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m10-v2-s-17-m-8.step) · [STL](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m10-v2-s-17-m-8.stl) — M10 DIN 557 square nut envelope (second table variant): 17 × 17 mm square (s), 8 mm thick (m), plain Ø10 bore at the thread major; corners are square, so the corner distance is 24.0 mm against the printed e max 24; no chamfer or thread
- square-nut-din-557-m12-s-18-m-10: [STEP](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m12-s-18-m-10.step) · [STL](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m12-s-18-m-10.stl) — M12 DIN 557 square nut envelope: 18 × 18 mm square (s), 10 mm thick (m), plain Ø12 bore at the thread major; corners are square, so the corner distance is 25.5 mm against the printed e max 25.4; no chamfer or thread
- square-nut-din-557-m12-v2-s-19-m-10: [STEP](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m12-v2-s-19-m-10.step) · [STL](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m12-v2-s-19-m-10.stl) — M12 DIN 557 square nut envelope (second table variant): 19 × 19 mm square (s), 10 mm thick (m), plain Ø12 bore at the thread major; corners are square, so the corner distance is 26.9 mm against the printed e max 26.9; no chamfer or thread
- square-nut-din-557-m16-s-24-m-13: [STEP](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m16-s-24-m-13.step) · [STL](https://xemstudio.com/files/hardware/square-nuts-din-557/square-nut-din-557-m16-s-24-m-13.stl) — M16 DIN 557 square nut envelope: 24 × 24 mm square (s), 13 mm thick (m), plain Ø16 bore at the thread major; corners are square, so the corner distance is 33.9 mm against the printed e max 33.9; no chamfer or thread

## Questions

**How big is an M6 square nut?**

10 mm across the square, 5 mm thick, 14.1 mm across corners max (fasten.it and CDE agree).

**Why are there two M10 square nut sizes?**

fasten.it prints 16 mm and 17 mm across flats rows for M10 (and 18 / 19 mm for M12) without explanation; CDE prints 17 and 19 only.

## Fits with

- [Hex nuts, M2–M8 (ISO 4032)](https://xemstudio.com/objects/hex-nuts-metric/)
- [Hex nuts, M10 to M24 (ISO 4032 / DIN 934)](https://xemstudio.com/objects/hex-nuts-metric-m10-m24/)
- [Slide-in T-nuts for 20, 30, 40, 45 mm and 1 in, 1.5 in T-slot extrusion](https://xemstudio.com/objects/slide-in-t-nuts/)
- [Drop-in T-nuts for 20, 30, 40, 45 mm and 1 in, 1.5 in T-slot extrusion](https://xemstudio.com/objects/drop-in-t-nuts/)
- [Hex flange nuts, DIN 6923: M3–M20 across flats, flange diameter, height, flange thickness + M5–M16 envelope files](https://xemstudio.com/objects/flange-nuts-din-6923/)
- [Acorn (domed cap) nuts, DIN 1587 high type: M4–M24 dome diameter, overall height, across flats, thread depth](https://xemstudio.com/objects/acorn-cap-nuts-din-1587/)