# Countersunk head screw (ISO 10642 / DIN 7991)

Hexagon socket countersunk (flat) head screw, metric coarse thread, M3 to M12, at any length. Presets cover the
common catalogue sizes (M3 × 8, M5 × 16, ...).

## Geometry

Envelope for assemblies and countersink checks:

- 90° countersunk head: the cone of the theoretical (sharp-edge) diameter **dk th** and height **k** = (dk th − d) / 2,
  its rim turned to the actual head diameter **dk min** (a short cylindrical land at the top), so the cone seats in a
  countersink exactly as the standard intends;
- hexagon socket, key size **s** (nominal), depth **t min**, flat bottom;
- plain shank at the nominal thread diameter **d**; the thread is not modelled.

`length` is the nominal length l, measured overall (head included) as ISO 10642 does; it must be at least k + 0.5 mm.
The head's top face is on the XY plane at the origin, the screw along -Z.

## Parameters

| Parameter | Meaning |
|---|---|
| `size` | Thread size, M3 to M12 |
| `length` | Nominal length l, overall, mm |
| `material` | `steel` (property class 8.8 to 12.9, black oxide), `stainless-a2`, `stainless-a4` (ISO 3506-1) |

## Source

ISO 10642:2004, *Hexagon socket countersunk head screws*, Table 1, p. 4: d, dk theoretical max, dk actual min, k max,
s (nominal), t min, read from the official preview
(<https://cdn.standards.iteh.ai/samples/34454/32dec7e84d974361b85f744935ab2175/ISO-10642-2004.pdf>; the M8 t is
under the preview's watermark and was read from fasten.it) and checked against fasten.it's DIN EN ISO 10642 2004-06
and 2013-04 tables (<https://fasten.it/en/Norms/Norm/DIN%20EN%20ISO%2010642>). Amendment 1:2012 changes only dk min of
M20 (not offered here).

Edition note: ISO 10642:2019 (DIN EN ISO 10642:2020-02; carried into ISO 10642:2026) replaced w min by t max and,
in fasten.it's reproduction of DIN EN ISO 10642:2020-02 (its only source found), lists smaller t min for M4 (1.4),
M5 (1.75), M8 (2.9) and M10 (3.5). This recipe models the 2004 edition's values, which are confirmed by the official
preview; every other column is the same in both.

| Size | dk th | dk min | k | s | t |
|---|---|---|---|---|---|
| M3 | 6.72 | 5.54 | 1.86 | 2.0 | 1.1 |
| M4 | 8.96 | 7.53 | 2.48 | 2.5 | 1.5 |
| M5 | 11.2 | 9.43 | 3.1 | 3.0 | 1.9 |
| M6 | 13.44 | 11.34 | 3.72 | 4.0 | 2.2 |
| M8 | 17.92 | 15.24 | 4.96 | 5.0 | 3.0 |
| M10 | 22.4 | 19.22 | 6.2 | 6.0 | 3.6 |
| M12 | 26.88 | 23.12 | 7.44 | 8.0 | 4.3 |

Preset list: sizes and lengths of the step.parts catalogue (MIT), see `library/NOTICE.md`.