ASME B18.3.1M Metric Socket Head Cap Screws

ASME B18.3.1M Metric Socket Head Cap Screws Dimensions

Metric Series Dimensions for Socket Head Cap Screws

ASME B18.3.1M standard provides dimensional and technical specifications for metric socket head cap screws, ensuring compatibility in metric-based systems and international applications. It includes details on head size, socket dimensions, thread pitch, and tolerances. This page offers detailed ASME B18.3.1M metric dimensions, along with size charts and engineering references.

Metric socket head cap screws per ASME B18.3.1M cover M3 through M48 diameters with internal-hex drive geometry. In ASTM A193 Grade B8 material, these are specified where European or globally-harmonised metric procurement is required and where the recessed Allen-drive head supports flush-mount or counterbored installation. ASME B18.3.1M is the SI equivalent of the inch-series B18.3 covered in dimensional detail elsewhere on this site.

ASME B18.3.1M Metric Socket Head Cap Screws Dimensions

Nom. Sizeand Thread Pitch	Body Diameter, D	Head Diameter A	Head Height H	Chamferor Radius S	Hexagon Socket Size^a J	Spline Socket Size^a M	Key Engagement T	Transition Dia. B^a
M1.6 × 0.35	1.6	1.46	3	2.87	1.6	1.52	0.16	1.5	1.829	0.8	2
M2 × 0.4	2	1.86	3.8	3.65	2	1.91	0.2	1.5	1.829	1	2.6
M2.5 × 0.45	2.5	2.36	4.5	4.33	2.5	2.4	0.25	2	2.438	1.25	3.1
M3 × 0.5	3	2.86	5.5	5.32	3	2.89	0.3	2.5	2.819	1.5	3.6
M4 × 0.7	4	3.82	7	6.8	4	3.88	0.4	3	3.378	2	4.7
M5 × 0.8	5	4.82	8.5	8.27	5	4.86	0.5	4	4.648	2.5	5.7
M6 × 1	6	5.82	10	9.74	6	5.85	0.6	5	5.486	3	6.8
M8 × 1.25	8	7.78	13	12.7	8	7.83	0.8	6	7.391	4	9.2
M10 × 1.5	10	9.78	16	15.67	10	9.81	1	8	...	5	11.2
M12 × 1.75	12	11.73	18	17.63	12	11.79	1.2	10	...	6	14.2
M14 × 2^b	14	13.73	21	20.6	14	13.77	1.4	12	...	7	16.2
M16 × 2	16	15.73	24	23.58	16	15.76	1.6	14	...	8	18.2
M20 × 2.5	20	19.67	30	29.53	20	19.73	2	17	...	10	22.4
M24 × 3	24	23.67	36	35.48	24	23.7	2.4	19	...	12	26.4
M30 × 3.5	30	29.67	45	44.42	30	29.67	3	22	...	15	33.4
M36 × 4	36	35.61	54	53.37	36	35.64	3.6	27	...	18	39.4
M42 × 4.5	42	41.61	63	62.31	42	41.61	4.2	32	...	21	45.6
M48 × 5	48	47.61	72	71.27	48	47.58	4.8	36	...	24	52.6
a See also Table 25. b The M14 ×2 size is not recommended for use in new designs. All dimensions are in millimeters LG is grip length and LB is body length. For length of complete thread. For additional manufacturing and acceptance specifications, see ASME B18.3.1M-1986.

Nom. Sizeand Thread Pitch

Body Diameter, D

Head Diameter A

Head Height H

Chamferor Radius S

Hexagon Socket Size^a J

Spline Socket Size^a M

Key Engagement T

Transition Dia. B^a

Max

Min.

Max

Min.

Max

Min.

Max

Nom.

Min.

Max

M1.6 × 0.35

1.6

1.46

2.87

1.6

1.52

0.16

1.5

1.829

0.8

M2 × 0.4

1.86

3.8

3.65

1.91

0.2

1.5

1.829

2.6

M2.5 × 0.45

2.5

2.36

4.5

4.33

2.5

2.4

0.25

2.438

1.25

3.1

M3 × 0.5

2.86

5.5

5.32

2.89

0.3

2.5

2.819

1.5

3.6

M4 × 0.7

3.82

6.8

3.88

0.4

3.378

4.7

M5 × 0.8

4.82

8.5

8.27

4.86

0.5

4.648

2.5

5.7

M6 × 1

5.82

9.74

5.85

0.6

5.486

6.8

M8 × 1.25

7.78

12.7

7.83

0.8

7.391

9.2

M10 × 1.5

9.78

15.67

9.81

...

11.2

M12 × 1.75

11.73

17.63

11.79

1.2

...

14.2

M14 × 2^b

13.73

20.6

13.77

1.4

...

16.2

M16 × 2

15.73

23.58

15.76

1.6

...

18.2

M20 × 2.5

19.67

29.53

19.73

...

22.4

M24 × 3

23.67

35.48

23.7

2.4

...

26.4

M30 × 3.5

29.67

44.42

29.67

...

33.4

M36 × 4

35.61

53.37

35.64

3.6

...

39.4

M42 × 4.5

41.61

62.31

41.61

4.2

...

45.6

M48 × 5

47.61

71.27

47.58

4.8

...

52.6

a See also Table 25.
b The M14 ×2 size is not recommended for use in new designs.
All dimensions are in millimeters
LG is grip length and LB is body length. For length of complete thread.
For additional manufacturing and acceptance specifications, see ASME B18.3.1M-1986.

Related Specifications

Surface Treatments

Xylan 1070 / 1014 / 1400 / 1424

Xylar 2 / 101

Geomet 321 / 500 / 720

SermaGard 1105 / 1280

Dacromet 320 / 500

TakeCoat 1000 Ceramic

Delta Tone/Seal

Magnigard

MolyKote

Sherardized

Zinc-Cobalt (ASTM B840)

Zinc-Nickel (ASTM B841)

Certifications

ISO 9001 - 2015 Certified
PED 2014/68/EC
NACE MR0175/ISO 15156-2
NORSOK M-650
DFAR
MERKBLATT AD 2000 W2/W7/W10

ASME B18.3.1M Metric Socket Head Cap Screws Dimensions