ASME B18.2.1 Askew Head Bolts

Scope

ASME B18.2.1 Askew Head Bolts dimension standard covers the dimensional requirements for product types of bolts and screws recognized as American National Standard. Also included are appendices covering gaging procedures, grade markings for bolts and screws, formulas on which dimensional data are based, and a specification to assist in identifying a product as being a screw or a bolt. Where questions arise concerning acceptance of product, the dimensions in the tables shall govern over recalculation by formula. Heavy hex structural bolts, formerly covered in ASME B18.2.1, are now covered in ASME B18.2.6, The Tables measurements are also converted into millimeters to make the information clearer and easier to to understand.

ASME B18.2.1 Askew Head Bolts Dimensions (mm)

Nominal Size		Body Diameter, E		Width Across Flats, F			Width Across Corners, G		Head Height, H1		Mid height, H	Radius of Fillet, R		Maximum Unthreaded Length, S	Nominal Thread Length for Bolt Lengths, LT
Nominal Size		Max.	Min.	Basic	Max.	Min.	Max.	Min.	Max.	Min.	Mid height, H	Max.	Min.	Maximum Unthreaded Length, S	152.4mm and Shorter	Over 152.4mm
3/8	0.3750	9.855	9.144	14.288	14.275	13.818	20.193	18.974	8.052	7.036	6.350	0.762	0.254	6.350	25.400	31.750
1/2	0.5000	13.081	12.243	19.050	19.050	18.415	26.949	25.273	10.439	9.423	8.331	0.762	0.254	7.925	31.750	38.100
5/8	0.6250	16.307	15.367	23.813	23.825	23.012	33.680	31.598	13.208	12.192	10.719	1.524	0.508	8.738	38.100	44.450
3/4	0.7500	19.507	18.517	28.575	28.575	27.635	40.411	37.948	15.596	14.580	12.700	1.524	0.508	10.312	44.450	50.800
7/8	0.8750	22.733	21.641	33.338	33.325	32.233	47.142	44.247	18.364	17.348	15.088	1.524	0.508	11.125	50.800	57.150
1	1.0000	25.959	24.790	38.100	38.100	36.830	53.873	50.571	20.345	19.329	16.662	2.286	0.762	12.700	57.150	63.500

ASME B18.2.1 Askew Head Bolts Length Tolerance (mm)

Nominal Length	Nominal Size (inches)
Nominal Length	1/4 to 3/8	7/16 and 1/2	9/16 to 3/4	7/8 and 1
Up to 25.4 mm, incl.	+0.508 0.762	+0.508 0.762	+0.508 0.762	...
Over 25.4 mm to 63.5 mm, incl.	+0.508 1.016	+1.016 1.524	+1.524 2.032	+2.032 2.54
Over 63.5 mm to 101.6 mm, incl.	+1.016 1.524	+1.524 2.032	+2.032 2.54	+2.54 3.556
Over 101.6 mm to 152.4 mm, incl.	+1.524 2.54	+2.032 2.54	+2.54 2.54	+3.048 4.064
Longer than 152.4 mm	+2.54 4.572	+3.048 4.572	+3.556 4.572	+4.064 5.08

ASME B18.2.1 Askew Head Bolts Grip Gaging Lengths (mm)

Nominal Size	Nominal Length, Lg, max. / Lb, min.
	1-1/4		1-3/8		1-1/2		1-5/8		1-3/4		1-7/8		2		2-1/8		2-1/4		2-3/8		2-1/2		2-5/8		2-3/4		2-7/8		3		3-1/4		3-1/2		3-3/4		4		4-1/4		4-1/2		4-3/4		5		5-1/4		5-1/2		5-3/4		6		6-1/4		6-1/2		6-3/4		7		7-1/4		7-1/2		7-3/4		8		8-1/4		8-1/2		8-3/4		9		9-1/4		9-1/2		9-3/4		10		11		12
	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.
3/8	Full thread		Full thread		12.70	4.83	15.75	7.87	19.05	11.18	22.35	14.22	25.40	17.53	28.45	20.57	31.75	23.88	35.05	26.92	38.10	30.23	41.15	33.27	44.45	36.58	47.75	39.62	50.80	42.93	57.15	49.28	63.50	55.63	69.85	61.98	76.20	68.33	82.55	74.68	88.90	81.03	95.25	87.38	101.60	93.73	107.95	100.08	114.30	106.43	120.65	112.78	127.00	119.13	127.00	119.13	133.35	125.48	139.70	131.83	146.05	138.18	152.40	144.53	158.75	150.88	165.10	157.23	171.45	163.58	177.80	169.93	184.15	176.28	190.50	182.63	196.85	188.98	203.20	195.33	209.55	201.68	215.90	208.03	222.25	214.38	247.65	239.78	273.05	265.18
1/2	Full thread		Full thread		Full thread		Full thread		Full thread		16.00	6.10	19.05	9.65	22.35	12.45	25.40	15.75	28.45	18.80	31.75	21.84	35.05	25.15	38.10	28.45	41.15	31.50	44.45	34.54	50.80	41.15	57.15	47.24	63.50	53.85	69.85	59.94	76.20	66.55	82.55	72.64	88.90	79.25	95.25	85.34	101.60	91.95	107.95	98.30	114.30	104.65	120.65	110.74	120.65	110.74	127.00	117.35	133.35	123.44	139.70	130.05	146.05	136.14	152.40	142.75	158.75	149.10	165.10	155.45	171.45	161.54	177.80	168.15	184.15	174.24	190.50	180.85	196.85	186.94	203.20	193.55	209.55	199.64	215.90	206.25	241.30	231.65	266.70	257.05
5/8	Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		19.05	7.62	22.35	10.67	25.40	13.97	28.45	17.02	31.75	20.32	35.05	23.37	38.10	26.67	44.45	33.02	50.80	39.37	57.15	45.72	63.50	52.07	69.85	58.42	76.20	64.77	82.55	71.12	88.90	77.47	95.25	83.82	101.60	90.17	107.95	96.52	114.30	102.87	114.30	102.87	120.65	109.22	127.00	115.57	133.35	121.92	139.70	128.27	146.05	134.62	152.40	140.97	158.75	147.32	165.10	153.67	171.45	160.02	177.80	166.37	184.15	172.72	190.50	179.07	196.85	185.42	203.20	191.77	209.55	198.12	234.95	223.52	260.35	248.92
3/4	Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		28.45	17.02	31.75	20.32	35.05	23.37	38.10	26.67	38.10	25.40	44.45	31.75	50.80	38.10	57.15	44.45	63.50	50.80	69.85	57.15	76.20	63.50	82.55	69.85	88.90	76.20	95.25	82.55	101.60	88.90	107.95	95.25	107.95	95.25	114.30	101.60	120.65	107.95	127.00	114.30	133.35	120.65	139.70	127.00	146.05	133.35	152.40	139.70	158.75	146.05	165.10	152.40	171.45	158.75	177.80	165.10	184.15	171.45	190.50	177.80	196.85	184.15	203.20	190.50	228.60	215.90	254.00	241.30
7/8	Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		25.40	12.70	28.45	15.75	31.75	19.05	31.75	17.53	38.10	23.88	44.45	30.23	50.80	36.58	57.15	42.93	63.50	49.28	69.85	55.63	76.20	61.98	82.55	68.33	88.90	74.68	95.25	81.03	101.60	87.38	101.60	87.38	107.95	93.73	114.30	100.08	120.65	106.43	127.00	112.78	133.35	119.13	139.70	125.48	146.05	131.83	152.40	138.18	158.75	144.53	165.10	150.88	171.45	157.23	177.80	163.58	184.15	170.18	190.50	176.28	196.85	182.63	222.25	208.03	247.65	233.43
1	Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		22.35	8.13	25.40	11.18	25.40	9.65	31.75	15.75	38.10	22.35	44.45	28.45	50.80	35.05	57.15	41.15	63.50	47.75	69.85	53.85	76.20	60.45	82.55	66.55	88.90	73.15	95.25	79.25	95.25	79.25	101.60	85.85	107.95	92.20	114.30	98.55	120.65	104.65	127.00	111.25	133.35	117.60	139.70	123.95	146.05	130.05	152.40	136.65	158.75	142.75	165.10	149.35	171.45	155.45	177.80	162.05	184.15	168.15	190.50	174.75	215.90	200.15	241.30	225.55

ASME B18.2.1 Askew Head Bolts Dimensions (Inch)

Nominal Size		Body Diameter, E		Width Across Flats, F			Width Across Corners, G		Head Height, H1		Mid height, H	Radius of Fillet, R		Maximum Unthreaded Length, S	Nominal Thread Length for Bolt Lengths, LT
Nominal Size		Max.	Min.	Basic	Max.	Min.	Max.	Min.	Max.	Min.	Mid height, H	Max.	Min.	Maximum Unthreaded Length, S	6 in. and Shorter	Over 6 in.
3/8	0.3750	0.388	0.360	9/16	0.562	0.544	0.795	0.747	0.317	0.277	0.250	0.03	0.01	0.250	1.000	1.250
1/2	0.5000	0.515	0.482	3/4	0.750	0.725	1.061	0.995	0.411	0.371	0.328	0.03	0.01	0.312	1.250	1.500
5/8	0.6250	0.642	0.605	15/16	0.938	0.906	1.326	1.244	0.520	0.480	0.422	0.06	0.02	0.344	1.500	1.750
3/4	0.7500	0.768	0.729	1 1/8	1.125	1.088	1.591	1.494	0.614	0.574	0.500	0.06	0.02	0.406	1.750	2.000
7/8	0.8750	0.895	0.852	1 5/16	1.312	1.269	1.856	1.742	0.723	0.683	0.594	0.06	0.02	0.438	2.000	2.250
1	1.0000	1.022	0.976	1 1/2	1.500	1.450	2.121	1.991	0.801	0.761	0.656	0.09	0.03	0.500	2.250	2.500

ASME B18.2.1 Askew Head Bolts Length Tolerance (Inch)

Nominal Length	Nominal Size
Nominal Length	1/4 to 3/8	7/16 and 1/2	9/16 to 3/4	7/8 and 1
Up to 1 in., incl.	+0.02 0.03	+0.02 0.03	+0.02 0.03	...
Over 1 in. to 2 1/2 in., incl.	+0.02 0.04	+0.04 0.06	+0.06 0.08	+0.08 0.10
Over 2 1/2 in. to 4 in., incl.	+0.04 0.06	+0.06 0.08	+0.08 0.10	+0.10 0.14
Over 4 in. to 6 in., incl.	+0.06 0.10	+0.08 0.10	+0.10 0.10	+0.12 0.16
Longer than 6 in.	+0.10 0.18	+0.12 0.18	+0.14 0.18	+0.16 0.20

ASME B18.2.1 Askew Head Bolts Grip Gaging Lengths (Inch)

Nominal Size	Nominal Length, Lg, max. / Lb, min.
	1-1/4		1-3/8		1-1/2		1-5/8		1-3/4		1-7/8		2		2-1/8		2-1/4		2-3/8		2-1/2		2-5/8		2-3/4		2-7/8		3		3-1/4		3-1/2		3-3/4		4		4-1/4		4-1/2		4-3/4		5		5-1/4		5-1/2		5-3/4		6		6-1/4		6-1/2		6-3/4		7		7-1/4		7-1/2		7-3/4		8		8-1/4		8-1/2		8-3/4		9		9-1/4		9-1/2		9-3/4		10		11		12
	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.	L_g Max.	L_b Min.
3/8	Full thread		Full thread		0.50	0.19	0.62	0.31	0.75	0.44	0.88	0.56	1.00	0.69	1.12	0.81	1.25	0.94	1.38	1.06	1.50	1.19	1.62	1.31	1.75	1.44	1.88	1.56	2.00	1.69	2.25	1.94	2.50	2.19	2.75	2.44	3.00	2.69	3.25	2.94	3.50	3.19	3.75	3.44	4.00	3.69	4.25	3.94	4.50	4.19	4.75	4.44	5.00	4.69	5.00	4.69	5.25	4.94	5.50	5.19	5.75	5.44	6.00	5.69	6.25	5.94	6.50	6.19	6.75	6.44	7.00	6.69	7.25	6.94	7.50	7.19	7.75	7.44	8.00	7.69	8.25	7.94	8.50	8.19	8.75	8.44	9.75	9.44	10.75	10.44
1/2	Full thread		Full thread		Full thread		Full thread		Full thread		0.63	0.24	0.75	0.38	0.88	0.49	1.00	0.62	1.12	0.74	1.25	0.86	1.38	0.99	1.50	1.12	1.62	1.24	1.75	1.36	2.00	1.62	2.25	1.86	2.50	2.12	2.75	2.36	3.00	2.62	3.25	2.86	3.50	3.12	3.75	3.36	4.00	3.62	4.25	3.87	4.50	4.12	4.75	4.36	4.75	4.36	5.00	4.62	5.25	4.86	5.50	5.12	5.75	5.36	6.00	5.62	6.25	5.87	6.50	6.12	6.75	6.36	7.00	6.62	7.25	6.86	7.50	7.12	7.75	7.36	8.00	7.62	8.25	7.86	8.50	8.12	9.50	9.12	10.50	10.12
5/8	Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		0.75	0.30	0.88	0.42	1.00	0.55	1.12	0.67	1.25	0.80	1.38	0.92	1.50	1.05	1.75	1.30	2.00	1.55	2.25	1.80	2.50	2.05	2.75	2.30	3.00	2.55	3.25	2.80	3.50	3.05	3.75	3.30	4.00	3.55	4.25	3.80	4.50	4.05	4.50	4.05	4.75	4.30	5.00	4.55	5.25	4.80	5.50	5.05	5.75	5.30	6.00	5.55	6.25	5.80	6.50	6.05	6.75	6.30	7.00	6.55	7.25	6.80	7.50	7.05	7.75	7.30	8.00	7.55	8.25	7.80	9.25	8.80	10.25	9.80
3/4	Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		1.12	0.67	1.25	0.80	1.38	0.92	1.50	1.05	1.50	1.00	1.75	1.25	2.00	1.50	2.25	1.75	2.50	2.00	2.75	2.25	3.00	2.50	3.25	2.75	3.50	3.00	3.75	3.25	4.00	3.50	4.25	3.75	4.25	3.75	4.50	4.00	4.75	4.25	5.00	4.50	5.25	4.75	5.50	5.00	5.75	5.25	6.00	5.50	6.25	5.75	6.50	6.00	6.75	6.25	7.00	6.50	7.25	6.75	7.50	7.00	7.75	7.25	8.00	7.50	9.00	8.50	10.00	9.50
7/8	Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		1.00	0.50	1.12	0.62	1.25	0.75	1.25	0.69	1.50	0.94	1.75	1.19	2.00	1.44	2.25	1.69	2.50	1.94	2.75	2.19	3.00	2.44	3.25	2.69	3.50	2.94	3.75	3.19	4.00	3.44	4.00	3.44	4.25	3.69	4.50	3.94	4.75	4.19	5.00	4.44	5.25	4.69	5.50	4.94	5.75	5.19	6.00	5.44	6.25	5.69	6.50	5.94	6.75	6.19	7.00	6.44	7.25	6.89	7.50	6.94	7.75	7.19	8.75	8.19	9.75	9.19
1	Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		Full thread		0.88	0.32	1.00	0.44	1.00	0.38	1.25	0.62	1.50	0.88	1.75	1.12	2.00	1.38	2.25	1.62	2.50	1.88	2.75	2.12	3.00	2.38	3.25	2.62	3.50	2.88	3.75	3.12	3.75	3.12	4.00	3.38	4.25	3.63	4.50	3.88	4.75	4.12	5.00	4.38	5.25	4.52	5.50	4.88	5.75	5.12	6.00	5.38	6.25	5.62	6.50	5.88	6.75	6.12	7.00	6.38	7.25	6.62	7.50	6.88	8.50	7.88	9.50	8.88

ASME Material Specifications

ASTM A193/A193M Standard Specification for Alloy-Steel and Stainless Steel Bolting Materials for High Temperature or High Pressure Service and Other Special Purpose Applications
ASTM A307 Standard Specification for Carbon Steel Bolts and Studs, 60 000 PSI Tensile Strength
ASTM A449 Standard Specification for Hex Cap Screws, Bolts and Studs, Steel, Heat Treated, 120/105/90 ksi Minimum Tensile Strength
ASTM A453/A453M Standard Specification for Bolting, Stud Bolts, Screws, Nuts
ASTM A354 Standard Specification for Quenched and Tempered Alloy Steel Bolts, Studs, and Other Externally Threaded Fasteners
ASTM A320 Standard Specification for Alloy-Steel and Stainless Steel Bolting for Low-Temperature Service
ASTM A1082/A1082M Standard Specification for Bolting, Stud Bolts, Screws, Nuts
ASTM A1014/A1014M Standard Specification for UNS N07718 Bolting, Stud Bolts, Screws, Nuts
ASTM F468 Standard Specification for Nonferrous Bolts, Hex Cap Screws, and Studs
ASTM F593 Standard Specification for Stainless Steel Bolts, Hex Cap Screws, and Studs
ASTM F901 Aluminium Transmission Tower Bolts
ASTM F738 Stud Bolts, Screws
ASTM F1554 Anchor Bolts, Anchor Rods
ASTM F2281 Bolting, Stud Bolts, Screws, Hex Cap Screws, Threaded Rods
ASTM F3125 Heavy Hex Bolts, Screws, Studs