DIN 912 – Hexagon Socket Cap Head Screw Dimensions

DIN 912 is the industrial standard for hexagon socket head cap screws, also known as Allen bolts. These high-strength fasteners feature a cylindrical head with an internal hexagonal drive, allowing for high torque application in confined spaces where a traditional hex bolt would be inaccessible.

While DIN 912 is the historical German standard, it has been functionally replaced by ISO 4762. Both standards are considered interchangeable for the vast majority of engineering applications, sharing identical dimensions for head diameter (dk), head height (k), and socket size (s).

DIN 912 Hexagon Socket Head Cap Screw Schematic

DIN 912 - Dimensions
Thread Size		M1.4	M1.6	M2	M2.5	M3	M4	M5	M6	M8	M10	M12	M14	M16	M18	M20	M22	M24	M27	M30	M33	M36	M42	M48	M56	M64	M72	M80	M90	M100
dk	Max	2.74	3.14	3.98	4.68	5.68	7.22	8.72	10.22	13.27	16.27	18.27	21.33	24.33	27.33	30.33	33.39	36.39	40.39	45.39	50.39	54.46	63.46	72.46	84.54	96.54	108.54	120.54	135.63	150.63
dk	Min	2.46	2.86	3.62	4.32	5.32	6.78	8.28	9.78	12.73	15.73	17.73	20.67	23.67	26.67	29.67	32.61	35.61	39.61	44.61	49.61	53.54	62.54	71.54	83.46	95.46	107.46	119.46	134.37	149.37
k	Max	1.4	1.6	2	2.5	3	4	5	6	8	10	12	14	16	18	20	22	24	27	30	33	36	42	48	56	64	72	80	90	100
k	Min	1.26	1.46	1.86	2.36	2.86	3.82	4.82	5.7	7.64	9.64	11.57	13.57	15.57	17.57	19.48	21.48	23.48	26.48	29.48	32.38	35.38	41.38	47.38	55.26	63.26	71.26	79.26	89.13	99.13
s	Nom	1.3	1.5	1.5	2	2.5	3	4	5	6	8	10	12	14	14	17	17	19	19	22	24	27	32	36	41	46	55	65	75	85
	Max	1.36	1.58	1.58	2.08	2.58	3.08	4.095	5.14	6.14	8.175	10.175	12.212	14.212	14.212	17.23	17.23	19.275	19.275	22.275	24.275	27.275	32.33	36.33	41.33	46.33	55.4	65.4	75.4	85.47
	Min	1.32	1.52	1.52	2.02	2.52	3.02	4.02	5.02	6.02	8.025	10.025	12.032	14.032	14.032	17.05	17.05	19.065	19.065	22.065	24.065	27.065	32.08	36.08	41.08	46.08	55.1	65.1	75.1	85.12
e	Min	1.5	1.733	1.733	2.303	2.873	3.443	4.583	5.723	6.863	9.149	11.429	13.716	15.996	16	19.437	19.44	21.734	21.73	25.154	27.43	30.854	36.571	41.131	46.831	52.531	62.81	74.21	85.61	97.04
t	Min	0.6	0.7	1	1.1	1.3	2	2.5	3	4	5	6	7	8	9	10	11	12	13.5	15.5	18	19	24	28	34	38	43	48	54	60
w	Min	0.5	0.55	0.55	0.85	1.15	1.4	1.9	2.3	3.3	4	4.8	5.8	6.8	7.8	8.6	9.4	10.4	11.9	13.1	13.5	15.3	16.3	17.5	19	22	25	27	32	34
r	Min	0.1	0.1	0.1	0.1	0.1	0.2	0.2	0.25	0.4	0.4	0.6	0.6	0.6	0.6	0.8	0.8	0.8	1	1	1	1	1.2	1.6	2	2	2	2	2.5	2.5
da	Max	1.8	2	2.6	3.1	3.6	4.7	5.7	6.8	9.2	11.2	13.7	15.7	17.7	20.2	22.4	24.4	26.4	30.4	33.4	36.4	39.4	45.6	52.6	63	71	79	87	97	107
ds	Max	1.4	1.6	2	2.5	3	4	5	6	8	10	12	14	16	18	20	22	24	27	30	33	36	42	48	56	64	72	80	90	100
ds	Min	1.26	1.46	1.86	2.36	2.86	3.82	4.82	5.82	7.78	9.78	11.73	13.73	15.73	17.73	19.67	21.67	23.67	26.67	29.67	32.61	35.61	41.61	47.61	55.54	63.54	71.54	79.54	89.46	99.46
dw	Min	2.32	2.72	3.48	4.18	5.07	6.53	8.03	9.38	12.33	15.33	17.23	20.17	23.17	25.87	28.87	31.81	34.81	38.61	43.61	48.61	52.54	61.34	70.34	82.26	94.26	106.26	118.16	133.17	148.17
b	Ref	14	15	16	17	18	20	22	24	28	32	36	40	44	48	52	56	60	66	72	78	84	96	108	124	140	156	172	192	212

Note: All measurement are in mm

Disclaimer: The dimensions presented on this page are based on the applicable industry standard. However, actual product measurements may vary slightly due to manufacturing practices, material selection, surface finish, and specified tolerance classes. Buyers and sourcing professionals are encouraged to verify final specifications with the manufacturer or supplier prior to procurement, particularly for critical applications.

Legend

dk – Head diameter.
da – Transition diameter (max).
ds – Shank diameter.
k – Head height.
s – Width across flats of the internal hexagon socket.
t – Minimum depth of the internal hexagon socket.
e – Width across corners of the internal hexagon socket (min).
dw – Minimum bearing diameter under the head.
b – Reference thread length.
r – Radius of the underhead fillet (min).
w – Minimum wall thickness between the socket and outer head diameter.
Ref (Reference value) – A theoretical dimension provided for information and design guidance only. Reference values (like b) are not requirements for inspection but assist in geometry calculation.

Technical Note

The maximum value of lg (overall screw length) can be determined by:
lg max = nominal length − b
where b is the reference thread length.
The minimum value of ls (unthreaded shank length) can be determined by:
ls min = lg max − 5P
where P is the thread pitch.
Standard nominal lengths (l) according to DIN 912 are generally available in the following ranges:
- For sizes M1.4 – M8: 2 mm to 80 mm
- For sizes M10 – M30: 16 mm to 200 mm
- For sizes M33 – M100: 50 mm to 300 mm

Standard Body Lengths and Tolerances
Nominal Length (l)	Min (mm)	Max (mm)
2.5 mm	2.3	2.7
3 mm	2.8	3.2
4 mm	3.76	4.24
5 mm	4.76	5.24
6 mm	5.76	6.24
8 mm	7.71	8.29
10 mm	9.71	10.29
12 mm	11.65	12.35
16 mm	15.65	16.35
20 mm	19.58	20.42
25 mm	24.58	25.42
30 mm	29.58	30.42
35 mm	34.5	35.5
40 mm	39.5	40.5
45 mm	44.5	45.5
50 mm	49.5	50.5
55 mm	54.4	55.6
60 mm	59.4	60.6
65 mm	64.4	65.6
70 mm	69.4	70.6
80 mm	79.4	80.6
90 mm	89.3	90.7
100 mm	99.3	100.7
110 mm	109.3	110.7
120 mm	119.3	120.7
130 mm	129.2	130.8
140 mm	139.2	140.8
150 mm	149.2	150.8
160 mm	159.2	160.8
180 mm	179.2	180.8
200 mm	199.075	200.925
220 mm	219.075	220.925
240 mm	239.075	240.925
260 mm	258.95	261.05
280 mm	278.95	281.05
300 mm	298.95	301.05

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