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(in˛)

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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