Free chart · ASME B18.2.1 · ISO 4014

Bolt size chart: hex and heavy hex.

Head dimensions for hex bolts, heavy hex bolts, hex cap screws and heavy hex screws from 1/4 to 4 in., and ISO metric hex bolts: the wrench size, width across the flats and corners, and head height, with the maximum and minimum the standard allows.

FWidth across flats: the wrench size is its basic (nominal) value.

GWidth across corners, point to point of the hex.

HHead height, from the bearing face to the top of the head.

Hex bolts, inch — ASME B18.2.1-2012

Nominal size (in.)	Threads per inch (UNC)	Wrench size (in.)	F — width across flats		G — width across corners		H — head height
Nominal size (in.)	Threads per inch (UNC)	Wrench size (in.)	Max.	Min.	Max.	Min.	Max.	Min.
1/4"	20	7/16	0.438	0.425	0.505	0.484	0.188	0.150
5/16"	18	1/2	0.500	0.484	0.577	0.552	0.235	0.195
3/8"	16	9/16	0.562	0.544	0.650	0.620	0.268	0.226
7/16"	14	5/8	0.625	0.603	0.722	0.687	0.316	0.272
1/2"	13	3/4	0.750	0.725	0.866	0.826	0.364	0.302
5/8"	11	15/16	0.938	0.906	1.083	1.033	0.444	0.378
3/4"	10	1-1/8	1.125	1.088	1.299	1.240	0.524	0.455
7/8"	9	1-5/16	1.312	1.269	1.516	1.447	0.604	0.531
1"	8	1-1/2	1.500	1.450	1.732	1.653	0.700	0.591
1-1/8"	7	1-11/16	1.688	1.631	1.949	1.859	0.780	0.658
1-1/4"	7	1-7/8	1.875	1.812	2.165	2.066	0.876	0.749
1-3/8"	6	2-1/16	2.062	1.994	2.382	2.273	0.940	0.810
1-1/2"	6	2-1/4	2.250	2.175	2.598	2.480	1.036	0.902
1-5/8"	8 UN	2-7/16	2.438	2.356	2.815	2.616	1.116	0.978
1-3/4"	5	2-5/8	2.625	2.538	3.031	2.893	1.196	1.054
1-7/8"	8 UN	2-13/16	2.812	2.719	3.248	3.099	1.276	1.130
2"	4.5	3	3.000	2.900	3.464	3.306	1.388	1.175
2-1/4"	4.5	3-3/8	3.375	3.262	3.897	3.719	1.548	1.327
2-1/2"	4	3-3/4	3.750	3.625	4.330	4.133	1.708	1.479
2-3/4"	4	4-1/8	4.125	3.988	4.763	4.546	1.869	1.632
3"	4	4-1/2	4.500	4.350	5.196	4.959	2.060	1.815
3-1/4"	4	4-7/8	4.875	4.712	5.629	5.372	2.251	1.936
3-1/2"	4	5-1/4	5.250	5.075	6.062	5.786	2.380	2.057
3-3/4"	4	5-5/8	5.625	5.437	6.495	6.198	2.572	2.241
4"	4	6	6.000	5.800	6.928	6.612	2.764	2.424

All dimensions in inches. Sizes marked 8 UN have no UNC thread and are threaded 8 UN. Wrench size = basic width across flats.

Heavy hex bolts, inch — ASME B18.2.1-2012

Nominal size (in.)	Threads per inch (UNC)	Wrench size (in.)	F — width across flats		G — width across corners		H — head height
Nominal size (in.)	Threads per inch (UNC)	Wrench size (in.)	Max.	Min.	Max.	Min.	Max.	Min.
3/8"	16	11/16	0.688	0.669	0.794	0.763	0.268	0.226
1/2"	13	7/8	0.875	0.850	1.010	0.969	0.364	0.302
5/8"	11	1-1/16	1.062	1.031	1.227	1.175	0.444	0.378
3/4"	10	1-1/4	1.250	1.212	1.443	1.383	0.524	0.455
7/8"	9	1-7/16	1.438	1.394	1.660	1.589	0.604	0.531
1"	8	1-5/8	1.625	1.575	1.876	1.796	0.700	0.591
1-1/8"	7	1-13/16	1.812	1.756	2.093	2.002	0.780	0.658
1-1/4"	7	2	2.000	1.938	2.309	2.209	0.876	0.749
1-3/8"	6	2-3/16	2.188	2.119	2.526	2.416	0.940	0.810
1-1/2"	6	2-3/8	2.375	2.300	2.742	2.622	1.036	0.902
1-5/8"	8 UN	2-9/16	2.562	2.481	2.959	2.829	1.116	0.978
1-3/4"	5	2-3/4	2.750	2.662	3.175	3.035	1.196	1.054
1-7/8"	8 UN	2-15/16	2.938	2.844	3.392	3.242	1.276	1.130
2"	4.5	3-1/8	3.125	3.025	3.608	3.449	1.388	1.175
2-1/4"	4.5	3-1/2	3.500	3.388	4.041	3.862	1.548	1.327
2-1/2"	4	3-7/8	3.875	3.750	4.474	4.275	1.708	1.479
2-3/4"	4	4-1/4	4.250	4.112	4.907	4.688	1.869	1.632
3"	4	4-5/8	4.625	4.475	5.340	5.102	2.060	1.815

All dimensions in inches. Sizes marked 8 UN have no UNC thread and are threaded 8 UN.

Hex cap screws (finished hex bolts), inch — ASME B18.2.1-2012

Nominal size (in.)	Threads per inch (UNC)	Wrench size (in.)	F — width across flats		G — width across corners		H — head height
Nominal size (in.)	Threads per inch (UNC)	Wrench size (in.)	Max.	Min.	Max.	Min.	Max.	Min.
1/4"	20	7/16	0.438	0.428	0.505	0.488	0.163	0.150
5/16"	18	1/2	0.500	0.489	0.577	0.557	0.211	0.195
3/8"	16	9/16	0.562	0.551	0.650	0.628	0.243	0.226
7/16"	14	5/8	0.625	0.612	0.722	0.698	0.291	0.272
1/2"	13	3/4	0.750	0.736	0.866	0.840	0.323	0.302
9/16"	12	13/16	0.812	0.798	0.938	0.910	0.371	0.348
5/8"	11	15/16	0.938	0.922	1.083	1.051	0.403	0.378
3/4"	10	1-1/8	1.125	1.100	1.299	1.254	0.483	0.455
7/8"	9	1-5/16	1.312	1.285	1.516	1.465	0.563	0.531
1"	8	1-1/2	1.500	1.469	1.732	1.675	0.627	0.591
1-1/8"	7	1-11/16	1.688	1.631	1.949	1.859	0.718	0.658
1-1/4"	7	1-7/8	1.875	1.812	2.165	2.066	0.813	0.749
1-3/8"	6	2-1/16	2.062	1.994	2.382	2.273	0.878	0.810
1-1/2"	6	2-1/4	2.250	2.175	2.598	2.480	0.974	0.902
1-5/8"	8 UN	2-7/16	2.438	2.356	2.815	2.686	1.038	0.962
1-3/4"	5	2-5/8	2.625	2.538	3.031	2.893	1.134	1.054
1-7/8"	8 UN	2-13/16	2.812	2.719	3.248	3.099	1.198	1.114
2"	4.5	3	3.000	2.900	3.464	3.306	1.263	1.175
2-1/4"	4.5	3-3/8	3.375	3.262	3.897	3.719	1.423	1.327
2-1/2"	4	3-3/4	3.750	3.625	4.330	4.133	1.583	1.479
2-3/4"	4	4-1/8	4.125	3.988	4.763	4.546	1.744	1.632
3"	4	4-1/2	4.500	4.350	5.196	4.959	1.935	1.815

All dimensions in inches. Sizes marked 8 UN have no UNC thread and are threaded 8 UN.

Heavy hex screws, inch — ASME B18.2.1-2012

Nominal size (in.)	Threads per inch (UNC)	Wrench size (in.)	F — width across flats		G — width across corners		H — head height
Nominal size (in.)	Threads per inch (UNC)	Wrench size (in.)	Max.	Min.	Max.	Min.	Max.	Min.
3/8"	16	11/16	0.688	0.669	0.794	0.763	0.243	0.226
1/2"	13	7/8	0.875	0.850	1.010	0.969	0.323	0.302
5/8"	11	1-1/16	1.062	1.031	1.227	1.175	0.403	0.378
3/4"	10	1-1/4	1.250	1.212	1.443	1.383	0.483	0.455
7/8"	9	1-7/16	1.438	1.394	1.660	1.589	0.563	0.531
1"	8	1-5/8	1.625	1.575	1.876	1.796	0.627	0.591
1-1/8"	7	1-13/16	1.812	1.756	2.093	2.002	0.718	0.658
1-1/4"	7	2	2.000	1.938	2.309	2.209	0.813	0.749
1-3/8"	6	2-3/16	2.188	2.119	2.526	2.416	0.878	0.810
1-1/2"	6	2-3/8	2.375	2.300	2.742	2.622	0.974	0.902
1-5/8"	8 UN	2-9/16	2.562	2.481	2.959	2.829	1.038	0.962
1-3/4"	5	2-3/4	2.750	2.662	3.175	3.035	1.134	1.054
1-7/8"	8 UN	2-15/16	2.938	2.844	3.392	3.242	1.198	1.114
2"	4.5	3-1/8	3.125	3.025	3.608	3.449	1.263	1.175
2-1/4"	4.5	3-1/2	3.500	3.388	4.041	3.862	1.423	1.327
2-1/2"	4	3-7/8	3.875	3.750	4.474	4.275	1.583	1.479
2-3/4"	4	4-1/4	4.250	4.112	4.907	4.688	1.744	1.632
3"	4	4-5/8	4.625	4.475	5.340	5.102	1.935	1.815
3-1/4"	4	5	5.000	4.838	5.774	5.515	2.126	1.998
3-1/2"	4	5-3/8	5.375	5.200	6.207	5.928	2.256	2.120
3-3/4"	4	5-3/4	5.750	5.562	6.640	6.341	2.447	2.303
4"	4	6-1/8	6.125	5.925	7.073	6.755	2.576	2.424

All dimensions in inches. Sizes marked 8 UN have no UNC thread and are threaded 8 UN.

Hex head bolts, metric — ISO 4014:2011

Size	Pitch (mm)	Wrench size (mm)	s — width across flats		e — across corners	k — head height		Product grade
Size	Pitch (mm)	Wrench size (mm)	Max.	Min.	Min.	Max.	Min.	Product grade
M5	0.8	8	8.000	7.780	8.790	3.650	3.350	A
M6	1	10	10.000	9.780	11.050	4.150	3.850	A
M8	1.25	13	13.000	12.730	14.380	5.450	5.150	A
M10	1.5	16	16.000	15.730	17.770	6.580	6.220	A
M12	1.75	18	18.000	17.730	20.030	7.680	7.320	A
M14	2	21	21.00	20.67	23.36	8.98	8.62	A
M16	2	24	24.000	23.670	26.750	10.180	9.820	A
M18	2.5	27	27.00	26.67	30.14	11.715	11.285	A
M20	2.5	30	30.000	29.670	33.530	12.715	12.285	A
M22	2.5	34	34.00	33.38	37.72	14.215	13.785	A
M24	3	36	36.000	35.380	39.980	15.215	14.785	A
M27	3	41	41.00	40.00	45.20	17.350	16.650	B
M30	3.5	46	46.000	45.000	50.850	19.120	18.280	B
M33	3.5	50	50.00	49.00	55.37	21.420	20.580	B
M36	4	55	55.000	53.800	60.790	22.920	22.080	B
M39	4	60	60.00	58.80	66.44	25.420	24.580	B
M42	4.5	65	65.000	63.100	71.300	26.420	25.580	B
M45	4.5	70	70.00	68.10	76.95	28.420	27.580	B
M48	5	75	75.000	73.100	82.600	30.420	29.580	B
M52	5	80	80.00	78.10	88.25	33.500	32.500	B
M56	5.5	85	85.000	82.800	93.560	35.500	34.500	B
M60	5.5	90	90.00	87.80	99.21	38.500	37.500	B
M64	6	95	95.000	92.800	104.860	40.500	39.500	B

All dimensions in mm, coarse thread. Product grade A to M24, grade B from M27. DIN 931 uses the same heads except across flats at M10 (17), M12 (19), M14 (22) and M22 (32 mm); see the wrench size chart.

Dimensions from ASME B18.2.1-2012 and ASME B18.2.2-2015 as printed in the IFI Book of Fastener Standards (2018) and cross-checked against the IFI Technology Connection; metric from ISO 4014:2011, ISO 4032:2012, DIN 931 and DIN 934. Body diameters, thread lengths and the other dimensions are on each product page, for example hex head bolts and heavy hex bolts.

Questions

Bolt sizes: common questions.

What are the dimensions of a 1/2 inch hex bolt?

Per ASME B18.2.1-2012, a 1/2-13 hex bolt has a 3/4 in. head: width across flats 0.750 to 0.725 in., across corners 0.866 to 0.826 in., and head height 0.364 to 0.302 in.

How is a heavy hex bolt different from a hex bolt?

A heavy hex bolt has a wider head for the same diameter, so it bears on more of the joint and takes a bigger wrench. A 1 in. hex bolt is 1-1/2 in. across the flats; a 1 in. heavy hex bolt is 1-5/8 in. The head heights are the same (0.700 to 0.591 in. at 1 in.).

What is the difference between a hex bolt and a hex cap screw?

A hex cap screw (formerly called a finished hex bolt) is made to tighter tolerances, with a washer face under the head and a closer body diameter. Its head is the same width across the flats but slightly lower: a 1/2 in. hex cap screw head is 0.323 to 0.302 in. high, against 0.364 to 0.302 in. for a hex bolt.

What wrench fits a 1/2 inch bolt?

3/4 in. for a standard hex bolt or cap screw and 7/8 in. for a heavy hex bolt. See the wrench size chart for every size.

More free tools

Need hex or heavy hex bolts made?

Made in Houston to ASME, ASTM and your drawing, with certs to the heat · quotes in 24 to 48 hours · 832-446-3442

Get a Quote

Bolt size chart: hex and heavy hex.

Bolt sizes: common questions.

Engineering tools from our shop.

Bolt torque calculator

Heavy hex nut chart

Wrench size chart

Need hex or heavy hex bolts made?