Bolt Dimensions Chart

Quick Answer: Bolt dimensions include the nominal diameter, head height, width across flats (wrench size), width across corners, and thread length. Imperial hex bolt dimensions follow ASME B18.2.1; metric hex bolts follow ISO 4014/4017. For stud bolts used in flanged piping, the key dimension is the thread diameter combined with the overall length per ASME B16.5.

Imperial Hex Bolt Dimensions (ASME B18.2.1)

These dimensions apply to standard heavy hex bolts, the type used in structural and piping applications with ASTM A193 B7 and similar grades.

Nominal Size	Width Across Flats (in)	Width Across Corners (in)	Head Height (in)	Thread Length - up to 6” bolt (in)
1/2”	7/8 (0.875)	1.010	21/64 (0.328)	1.00
5/8”	1-1/16 (1.062)	1.227	27/64 (0.422)	1.25
3/4”	1-1/4 (1.250)	1.443	15/32 (0.469)	1.38
7/8”	1-7/16 (1.438)	1.660	35/64 (0.547)	1.50
1”	1-5/8 (1.625)	1.876	39/64 (0.609)	1.75
1-1/8”	1-13/16 (1.812)	2.093	11/16 (0.688)	2.00
1-1/4”	2 (2.000)	2.309	25/32 (0.781)	2.00
1-3/8”	2-3/16 (2.188)	2.526	27/32 (0.844)	2.25
1-1/2”	2-3/8 (2.375)	2.742	15/16 (0.938)	2.25
1-3/4”	2-3/4 (2.750)	3.175	1-3/32 (1.094)	2.50
2”	3-1/8 (3.125)	3.608	1-7/32 (1.219)	2.75
2-1/4”	3-1/2 (3.500)	4.041	1-3/8 (1.375)	3.00
2-1/2”	3-7/8 (3.875)	4.474	1-17/32 (1.531)	3.25
3”	4-5/8 (4.625)	5.340	1-13/16 (1.812)	3.50

Metric Hex Bolt Dimensions (ISO 4014)

Nominal Size	Width Across Flats (mm)	Width Across Corners (mm)	Head Height (mm)	Thread Length - up to 125 mm bolt (mm)
M6	10	11.05	4.0	18
M8	13	14.38	5.3	22
M10	16	18.90	6.4	26
M12	18	20.03	7.5	30
M14	21	23.35	8.8	34
M16	24	26.75	10.0	38
M18	27	29.56	11.5	42
M20	30	32.95	12.5	46
M22	34	37.29	14.0	50
M24	36	39.55	15.0	54
M27	41	45.20	17.0	60
M30	46	50.85	18.7	66
M33	50	55.37	21.0	72
M36	55	60.79	22.5	78
M42	65	71.30	26.0	90
M48	75	82.60	30.0	102

Heavy Hex Nut Dimensions

Nut dimensions must match the bolt’s width across flats. For piping, ASTM A194 Grade 2H heavy hex nuts are standard.

Bolt Size	Nut Width Across Flats (in)	Nut Height (in)
1/2”	7/8	31/64
5/8”	1-1/16	39/64
3/4”	1-1/4	47/64
7/8”	1-7/16	55/64
1”	1-5/8	63/64
1-1/8”	1-13/16	1-7/64
1-1/4”	2	1-7/32
1-3/8”	2-3/16	1-11/32
1-1/2”	2-3/8	1-15/32
2”	3-1/8	1-29/32

Common Mistake

Do not confuse standard hex bolt dimensions with heavy hex bolt dimensions. Piping specifications (ASME B16.5, B16.47) require heavy hex bolts and nuts, which have larger across-flats dimensions than standard hex fasteners. Using standard hex nuts on heavy hex stud bolts will not engage properly.

Stud Bolt Dimensions

Stud bolts differ from hex bolts; they are fully threaded rods without a head. The critical dimensions are the nominal thread diameter, thread pitch (8UN for sizes 1” and above per ASME B16.5), and overall length. Stud bolt lengths for each flange size and pressure class include the thickness of both flanges, the gasket, and two heavy hex nuts plus allowance for thread protrusion.

Proper bolt sizing ensures adequate thread engagement and allows the application of correct torque to achieve target gasket compression.

Read the full guide to stud bolts for flanges