Suggested Tightening Torque

Suggested Tightening Torque Values to Produce Corresponding Bolt Clamping Loads

			SAE Grade 2 Bolts					SAE Grde 5 Bolts					SAE Grade 7			SAE Grade 8
Size	Bolt Diam. D(in.)	Stress Area A(in²)	Tensile Strngth min psi	Proof Load psi	Clamp Loa P (lb)	T Dry	Tor- que Lub.	Tensile Strength	Proof Load	Clamp Load	T Dry	Tor -que Lub.	Clamp Load	Tight Dry	Tor- que Lub.	Clamp Load	T Dry	Tor- que Lub.
4-40	0.1120	.00604	74,000	55,000	240	5	4	120,000	85,000	380	8	6	480	11	8	540	12	9
4-48	0.1120	.00661			280	6	5			420	9	7	520	12	9	600	13	10
6-32	0.1380	.00909			380	10	8			580	16	12	720	20	15	820	23	17
6-40	0.1380	.01015			420	12	9			640	18	13	800	22	17	920	25	19
8-32	0.1640	.01400			580	19	14			900	30	22	1100	36	27	1260	41	31
8-36	0.1640	.01474			600	20	15			940	31	23	1160	38	29	1320	43	32
10-24	0.1900	.01750			720	27	21			1120	43	32	1380	52	39	1580	60	45
10-32	0.1900	.02000			820	31	23			1285	49	36	1580	60	45	1800	68	51
1/4-20	0.2500	0.0318			1320	66	49			2020	96	75	2500	120	96	2860	144	108
1/4-28	0.2500	0.0364			1500	76	56			2320	120	86	2880	144	108	3280	168	120
5/16-18	0.3125	0.0524			2160	11	8			3340	17	13	4120	21	16	4720	25	18
5/16-24	0.3125	0.0580			2400	12	9			3700	19	14	4580	24	18	5220	25	20
3/8-16	0.3750	0.0775			3200	20	15			4940	30	23	6100	40	30	7000	45	35
3/8-24	0.3750	0.0878			3620	23	17			5600	35	25	6900	41	30	7900	50	35
7/16-14	0.4375	0.1063			4380	30	24			6800	50	35	8400	60	45	9550	70	55

7/16-20	0.4375	0.1187			4900	35	25			7550	55	40	9350	70	50	10700	80	60
1/2-13	0.5000	0.1419			5840	50	35			9050	75	55	11200	95	70	12750	110	80
1/2-13	0.5000	0.1599			6600	55	40			10700	90	65	12600	100	80	14400	120	90
9/16-12	0.5625	0.1820			7500	70	55			11600	110	80	14350	135	100	16400	150	110
9/16-18	0.5625	0.2030			8400	80	60			12950	120	90	16000	150	110	18250	170	130

5/8-11	0.6250	0.2260			9300	100	75			14400	150	110	17800	190	140	20350	220	170
5/8-18	0.6250	0.2560			10600	110	85			16300	170	130	20150	210	160	23000	240	180
3/4-10	0.7500	0.3340			13800	175	130			21300	260	200	26300	320	240	30100	380	280
3/4-16	0.7500	0.3730			15400	195	145			23800	300	220	29400	360	280	33600	420	320
7/8-9	0.8750	0.4620	60,000	33,000	11400	165	125			29400	430	320	36400	520	400	41600	600	460

7/8-14	0.8750	0.5090			12600	185	140			32400	470	350	40100	580	440	45800	660	500
1-8	1.0000	0.6060			15000	250	190			38600	640	480	47700	800	600	54500	900	680
1-12	1.0000	0.6630			16400	270	200			42200	700	530	52200	860	660	597	1100	740
1-1/4 7	1.1250	0.7630			18900	350	270	105,000	74,000	42300	800	600	60100	1120	840	68700	1280	960
1-1/4 12	1.1250	0.8560			21200	400	300			47500	880	660	67400	1260	940	77000	1440	1080
1-1/4 7	1.2500	0.9690			24000	500	380			53800	1120	840	76300	1580	1100	87200	1820	1361
1-1/4 12	1.2500	1.0730			26600	550	420			59600	1240	920	84500	1760	1320	116600	2000	1500
1-3/8 6	1.3750	1.1550			28600	660	490			64100	1460	1100	91000	2080	1560	104000	2380	1780
1-3/812	1.3750	1.3150			32500	740	560			73000	1680	1260	104000	2380	1780	118400	2720	2040
1-3/8 6	1.5000	1.4050			34800	870	650			78000	1940	1460	111000	2780	2080	126500	3160	2360
1-1/2 12	1.5000	1.5800			39100	980	730			87700	2200	1640	124005	3100	2320	142200	3560	2660

Notes:

1. Tightening torque values are calculated from the formula T = KDP, where T= tightening torque. lb-in. K=torque-friction coefficient; D = nominal bolt diameter. in; and P = bolt clamp load developed by tightening. lb.

2. Clamp load is also known as preload or initial load in tension on bolt. Clamp load (lb) is calculated by arbitrarily assuming usable bolt strength is 75% of bolt proof load(psi) times tensile stress area(sq in.) of threaded section of each bolt size. Higher or lower values of clamp load can be used depending on the application requirements and the judgement of the designer.

3. Tensile strength (min psi) of all Grade 7 bolts is 133,000. Proof load is 105,000 psi.

4. Tensile strength (min psi) of all Grade 8 bolts is 150,000 psi. Proof load is 120,000 psi. Ref.:Fastening Reference, Machine Design, Nov 1977.

Bolt Clamping Force vs. Tightening Torque for Unlubricated Steel Bolts.

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