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DIN 7991

Countersunk head screw,hex drive

Superseded by ISO 10642 (2026), whose head differs · Still sold as DIN 7991 · Sizes M3–M24
DIN 7991 screw side view with the socket drawn dashed, showing d, P, dk, k, l and the socket depth tDIN 7991 screw side view with the socket drawn dashed, showing d, P, dk, k, l and the socket depth t
Side view
DIN 7991 screw seen from the head, with the socket size sDIN 7991 screw seen from the head, with the socket size s
Head view
SizeP (mm, coarse)dk (mm, max)k (mm, max)s (mm, nom.)t (mm, nom.)
M3
0.506.001.702.001.20
M4
0.708.002.302.501.80
M5
0.8010.002.803.002.30
M6
1.0012.003.304.002.50
M8
1.2516.004.405.003.50
M10
1.5020.005.506.004.40
M12
1.7524.006.508.004.60
M16
2.0030.007.5010.005.30
M20
2.5036.008.5012.005.90

Values per DIN 7991:1986.

Work out the screw length you needOpens the bolted joint configurator with DIN 7991 chosen.

Verified data

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About DIN 7991

What it is

A countersunk screw with a hexagon socket: the cone-shaped head sinks into a countersink and ends flush. Up to M20 the head has a 90° angle; M22 and M24 have 60°. An M10 has a 20 mm head and takes a 6 mm key.

Where it is used

On covers, guards, slides and any face where nothing may stick out, from M3 to M24.

DIN or ISO

ISO 10642 replaced DIN 7991, but the two heads are not the same: ISO 10642 gives a theoretical and an actual head diameter and a higher head. For that reason the site shows DIN 7991 alone for now.

Typical mistakes

  • Measuring the length under the head. A countersunk screw is measured overall, head included.
  • Cutting a 90° countersink for an M22 or M24, whose head is 60°.
  • Putting a washer under the head. The cone needs its countersink.
  • Expecting the full load of the strength class. ISO 898-1 and ISO 10642 give these screws a reduced load because of the head.
  • Swapping DIN 7991 for ISO 10642 without checking the countersink depth: the heads differ.

References