| Bolt Size TPI Tightening Torque Range (ft lbs) (Min – Max) | Plain | 3 ⁄ 4 10 350 – 425 | 7 ⁄ 8 9 569 – 685 | 1 8 850 – 1,017 |
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| Size Recommended Torque | Grade 2 | 9/16′′ 53 59 | 5/8′′ 73 83 | 3/4 “ 125 138 |
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| Bolt Size TPI Tension MIN | 7/8′′ 9 39,000 | 1′′ 8 51,000 | 1 1/8′′ 7 56,000 | 1 1/4′′ 7 71,000 |
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Begin with the formula T = K x U x D x P , where T is the torque, K is a standard representing 1.33, U is the coefficient of friction, D is the diameter of the fasteners, and P is the necessary preload.
Grade A325 bolts are available in diameters from 1/2 to 1-1/2 inch (for diameters greater than 1-1/2, ASTM A449 specifications should be considered) with a minimum tensile strength of 120,000 PSI .
Torque tightening is the accurate application of torque to a nut so that a bolt can hold its load securely without breaking.
| Product: 3/4-10 Grade 5 zinc plated bolt | • D= .750 (3/4-10 nominal diameter | • P= 23.046 pounds |
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For pretensioned joints, A325 bolts require a washer under the element (head or nut) being turned to tight- en the bolt . For pretensioned joints with specified base metal yield strength less than 40ksi, A490 and F2280 bolts require a washer under both the head and nut.
| Bolt Size TPI Tightening Torque (ft lbs) | Plain | 5 ⁄ 16 18 17 | 3 ⁄ 8 16 31 | 7 ⁄ 16 14 49 |
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Typically an A325 -A490 bolt when fully tensioned will destroy a lock washer. The washers are not needed in a fully tensioned connection . When bolts are place in a connection that is required to slip the threads are distressed or the nut is tacked to prevent loosening.
| GRADE 5 GRADE 8 | Coarse Thread Coarse Thread | 7/16-20 (.4375) 7575 7/16-20 (.4375) | 1/2-20 (.500) 10200 1/2-20 (.500) | 9/16-18 (.5625) 12975 9/16-18 (.5625) |
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The Torque/Tension Equation is a method used to estimate the torque/tension relationship in an assembly. T = (K D P)/12 can be used to developt a torque value that will achieve a certain tension or clamp load. T = Torque (ft. -lbs.)
Mark the tightened fastener and surrounding application . In the tightening direction, begin to slowly apply force to the tool until the first movement in the fastener is noted. The reading recorded is a good indication of the original torque applied to the joint. This is the best way to determine residual torque.
As a comparison, the ASTM A325 bolt is roughly equivalent to the SAE grade 5. A grade 8 bolt would be one that meets ASTM A490 standards. The A325 bolt strength, or SAE grade 5 bolt strength, is usually used for structural bolting projects.
Strength Differences
A325 bolts are typically manufactured from a medium carbon steel (although they can be made from an alloy) while SAE grade 8 bolts are made from a medium carbon alloy steel. Grade 8 bolts are significantly stronger than an A325 .
A490 bolts are more susceptible to brittle fracture than A325 bolts which are 120/105 minimum tensile strength steel. To minimize the risk of brittle fracture A490 bolts have both a minimum and a maximum tensile strength specified.
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