← AskMachinist · Guides · Calculator · 🔎 Search

Hex Head Screw Dimensions (ISO 4017 / DIN 933, M3 to M36)

Guide · Updated October 28, 2026

ISO 4017 covers hexagon head screws threaded up to the head, the everyday hex bolt in metric machine and fixture work (formerly DIN 933). The table gives coarse pitch, width across flats s (wrench size), nominal head height k, minimum width across corners e, minimum bearing face diameter dw and product grade. Head sizes agree between the ISO 4017:2022 preview tables, the RoyMech ISO hexagon bolt table and the fasteners.eu DIN 933 / ISO 4017 table. Check the current edition or your supplier for critical work.

Need an exact reference size?

Build any gage block stack with the free Gage Block Calculator. Free, no login.

Step by step

Read the thread: Measure the major diameter and check pitch with a thread gage. This chart covers coarse pitch M3 to M36.
Pick the wrench: Width across flats s is the wrench size: M6 10 mm, M8 13 mm, M10 16 mm, M12 18 mm. ISO sizes differ from older DIN 933 at M10, M12, M14 and M22.
Check head clearance: Head height k plus socket wall sets the counterbore depth or the clearance under a guard or fixture plate.
Check the spot face: Bearing face dw min tells you the smallest spot face or washer that fully supports the head.
Screw or bolt: ISO 4017 screws are threaded to the head. ISO 4014 bolts have a plain shank but the same head sizes.
Torque: Torque to the property class (8.8, 10.9) with a calibrated wrench; use a washer on soft or slotted parts.

ISO 4017 hex head screw dimensions (mm)

Columns: thread size, coarse pitch P, width across flats s (max, the wrench size), head height k (nominal), width across corners e min, bearing face diameter dw min, product grade. M3 to M24 are grade A values; M30 and M36 are grade B.

Size | P | s | k | e min | dw min | grade
M3 | 0.5 | 5.5 | 2.0 | 6.01 | 4.57 | A
M4 | 0.7 | 7 | 2.8 | 7.66 | 5.88 | A
M5 | 0.8 | 8 | 3.5 | 8.79 | 6.88 | A
M6 | 1 | 10 | 4.0 | 11.05 | 8.88 | A
M8 | 1.25 | 13 | 5.3 | 14.38 | 11.63 | A
M10 | 1.5 | 16 | 6.4 | 17.77 | 14.63 | A
M12 | 1.75 | 18 | 7.5 | 20.03 | 16.63 | A
M16 | 2 | 24 | 10.0 | 26.75 | 22.49 | A
M20 | 2.5 | 30 | 12.5 | 33.53 | 28.19 | A
M24 | 3 | 36 | 15.0 | 39.98 | 33.61 | A
M30 | 3.5 | 46 | 18.7 | 50.85 | 42.75 | B
M36 | 4 | 55 | 22.5 | 60.79 | 51.11 | B

Wrench quick list

ISO 4017 wrench by thread: M3 5.5 mm, M4 7 mm, M5 8 mm, M6 10 mm, M8 13 mm, M10 16 mm, M12 18 mm, M16 24 mm, M20 30 mm, M24 36 mm, M30 46 mm, M36 55 mm.

ISO vs DIN 933 head sizes

Across flats changed when DIN 933 moved to ISO 4017: M10 17 to 16 mm, M12 19 to 18 mm, M14 22 to 21 mm, M22 32 to 34 mm. Every other size listed here is the same. If a 16 mm socket spins on an M10 head, it is an old DIN head; grab a 17.

Worked example: counterbore for an M12 hex head

An M12 hex head screw has k 7.5 mm and e min 20.03 mm. A 12 point socket on an 18 mm head is about 25 mm OD, so a 26 mm counterbore 9 mm deep clears the head and the socket. If you only need a spot face, dw min is 16.63 mm, so any spot face of 18 mm or more supports the full bearing face.

Worked example: fixture plate guard clearance

Four M8 x 25 hex head screws hold a guard. Head height k is 5.3 mm; add a 1.6 mm ISO 7089 washer and the stack stands about 6.9 mm proud. Leave 8 mm under the cover so a 13 mm socket can reach.

Common problems

Socket rounds the head: wrong standard (DIN vs ISO) or a 12 point socket on a soft head. Use a 6 point of the right size.
Head sits crooked: spot face smaller than dw or not square to the hole.
Head will not clear a counterbore: sized for a socket head cap screw. Hex heads need room for the socket wall.
Bolt stretches or snaps: torque beyond the property class. Check the head marking (8.8, 10.9).

FAQ

What wrench fits an M10 hex bolt?

16 mm for ISO 4017. Old DIN 933 M10 heads are 17 mm, so keep both in the box.

Is ISO 4017 the same as DIN 933?

Nearly. Same thread and head heights, but ISO across flats are smaller at M10 (16 vs 17), M12 (18 vs 19), M14 (21 vs 22) and M22 (34 vs 32).

What is the difference between ISO 4014 and ISO 4017?

ISO 4017 is threaded all the way to the head. ISO 4014 has a plain shank. Head dimensions are the same.

What do product grades A and B mean?

Tolerance classes. Grade A is the tighter class used here through M24; M30 and M36 are grade B values.

Related guides and calculators

Build your stack in seconds

The free Gage Block Calculator finds the fewest-block combination for inch and metric sets, with wear blocks. No login.

Questions? Ask a machinist.

General shop information only — follow your drawing, tool maker's data and your quality system.