7/8 inch bolt torque specifications (Grade 2, 5, 8)
A 7/8-9 Grade 5 bolt takes 430 ft-lb (582 N·m) and a Grade 8 takes 606 ft-lb (822 N·m). Both values are for plain, dry steel threads (K 0.20) tightened to 75% of proof load.
Contents12 sections
Key takeaways
- Grade 2 drops to 33,000 psi proof above 3/4 in 1, so a 7/8-9 Grade 2 is only 167 ft-lb dry, less than a 3/4-10 Grade 2.
- At 7/8 in a Grade 5 bolt carries 2.6 times the clamp load of a Grade 2.
- Oiled threads need 25% less torque for the same clamp load (K 0.15 vs 0.20) 1: 322 ft-lb for Grade 5, 455 ft-lb for Grade 8.
- Hex cap screw and nut 1-5/16 in; structural heavy hex 1-7/16 in 1.
Quick facts
| Coarse thread | 7/8-9 UNC |
|---|---|
| Fine thread | 7/8-14 UNF |
| Wrench, hex cap screw and nut | 1-5/16 in |
| Wrench, heavy hex bolt | 1-7/16 in |
7/8 in bolt specifications
| Thread | Pitch | Tensile stress area |
|---|---|---|
| 7/8-9 (UNC) | 9 threads per inch | 0.4620 in² |
| 7/8-14 (UNF) | 14 threads per inch | 0.5100 in² |
| Wrench, hex cap screw | 1-5/16 in1 | |
| Wrench, heavy hex (structural) | 1-7/16 in | |
Stress areas from ASME B1.1 as tabulated by Fastenal1.
7/8 in torque by grade
| Grade | Plain, dry K 0.201 | Lubricated K 0.151 | Clamp load |
|---|---|---|---|
| Grade 2 | 167 ft-lb226 N·m | 125 ft-lb170 N·m | 11,430 lbf |
| Grade 5 | 430 ft-lb582 N·m | 322 ft-lb437 N·m | 29,450 lbf |
| Grade 8 | 606 ft-lb822 N·m | 455 ft-lb617 N·m | 41,580 lbf |
Calculated with T = K × D × F, where F is 75% of the bolt’s proof load1 and K is the nut factor for each condition. Real preload from a torque wrench scatters by about ±25%2. When the equipment maker gives a torque, use theirs. How these numbers are made.
7/8 in Grade 2 torque
Proof 33,000 psi · yield 36,000 psi · tensile 60,000 psi1. Clamp load at 75% of proof: 11,430 lbf (7/8-9).
| Condition | K | 7/8-9 | 7/8-14 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 167 ft-lb226 N·m | 184 ft-lb250 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 150 ft-lb203 N·m | 166 ft-lb225 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 125 ft-lb170 N·m | 138 ft-lb187 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.163 | 133 ft-lb181 N·m | 147 ft-lb200 N·m |
| Moly pasteMolybdenum disulfide paste | 0.114 | 92 ft-lb124 N·m | 101 ft-lb137 N·m |
7/8 in Grade 5 torque
Proof 85,000 psi · yield 92,000 psi · tensile 120,000 psi1. Clamp load at 75% of proof: 29,450 lbf (7/8-9).
| Condition | K | 7/8-9 | 7/8-14 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 430 ft-lb582 N·m | 474 ft-lb643 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 387 ft-lb524 N·m | 427 ft-lb579 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 322 ft-lb437 N·m | 356 ft-lb482 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.163 | 344 ft-lb466 N·m | 379 ft-lb514 N·m |
| Moly pasteMolybdenum disulfide paste | 0.114 | 236 ft-lb320 N·m | 261 ft-lb354 N·m |
7/8 in Grade 8 torque
Proof 120,000 psi · yield 130,000 psi · tensile 150,000 psi1. Clamp load at 75% of proof: 41,580 lbf (7/8-9).
| Condition | K | 7/8-9 | 7/8-14 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 606 ft-lb822 N·m | 669 ft-lb908 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 546 ft-lb740 N·m | 602 ft-lb817 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 455 ft-lb617 N·m | 502 ft-lb681 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.163 | 485 ft-lb658 N·m | 536 ft-lb726 N·m |
| Moly pasteMolybdenum disulfide paste | 0.114 | 334 ft-lb452 N·m | 368 ft-lb499 N·m |
Grade 2 changes at this size
SAE J429 splits Grade 2 at 3/4 in. Up to 3/4 in it has 55,000 psi proof, 57,000 psi yield and 74,000 psi tensile; from 7/8 in it drops to 33,000, 36,000 and 60,000 psi 1. Grade 5 and Grade 8 keep their full strength here (85,000 and 120,000 psi proof) 1.
The result shows in the chart. A 7/8-9 Grade 2 clamps 11,430 lbf at 167 ft-lb dry, while the smaller 3/4-10 Grade 2 clamps 13,820 lbf at 173 ft-lb. Between grades the spread widens: Grade 5 at 7/8 in carries 29,450 lbf, 2.6 times the Grade 2 figure, against 1.55 times at 3/4 in and below. An unmarked 7/8 in bolt torqued to a Grade 5 value would be asked to carry nearly twice its proof load. If the head has no radial lines, use the Grade 2 row.
Which grade you have
Grade 2 heads are plain, Grade 5 shows three radial lines, Grade 8 six 1. Use a Grade 5 nut on a Grade 5 bolt and a Grade 8 nut on a Grade 8 bolt 1. The grades page shows the markings and the Grade 2 page lists both strength rows.
Coarse or fine thread
The 7/8-9 coarse thread has a tensile stress area of 0.462 in²; the 7/8-14 fine thread has 0.510 in² 1. The fine thread carries 10.4% more clamp load at the same stress: 474 against 430 ft-lb in Grade 5 dry, 669 against 606 ft-lb in Grade 8. The printed fine-thread area is Fastenal’s; the ASME B1.1 formula gives 0.5095 in² 5, too small a difference to change the rounded torques.
Structural bolts at 7/8 in
A325 and A490 heavy hex bolts of this diameter are pretensioned to RCSC minimums of 39 kips for A325 and 49 kips for A490 6. The A325 figure is above the Grade 5 chart clamp (29,450 lbf); the A490 figure is above the Grade 8 one (41,580 lbf). RCSC does not allow table or formula torques without verification for calibrated-wrench installation 6. See A325 bolt torque.
When the chart does not apply
The values size clamp load to the bolt’s proof load with the K in each row. They do not check whether the clamped parts or a tapped hole can carry 11,000 to 46,000 lbf, and preload from a torque wrench scatters by about ±25% 2. When the equipment maker gives a torque, use the maker’s value; for lubricated threads see dry vs lubricated torque.
Sources
- 1
- 2
- 3
- 4Henkel Corporation (LOCTITE), LOCTITE LB 8012 Moly Paste TDS, April 2015Checked 21 Oct 2026
- 5
- 6
Spotted a value that doesn’t match its source? Report an error
Related
- 3/4 in3/4-10 Grade 5 bolt torque is 267 ft-lb dry and Grade 8 is 377 ft-lb. Charts for 3/4-10 and 3/4-16 in Grade 2, 5 and 8, dry, zinc-plated and oiled.
- 1 in1-8 Grade 5 bolt torque is 644 ft-lb dry and Grade 8 is 909 ft-lb. Charts for 1-8 and 1-12 in Grade 2, 5 and 8, dry, zinc-plated and oiled.
- Grade 2Grade 2 bolt torque from 1/4 in to 1 in, dry, zinc-plated and lubricated, with SAE J429 strength, the drop to 33 ksi proof above 3/4 in, and the plain-head marking.
- Grade 5Grade 5 bolt torque from 1/4 in to 1 in, dry, zinc-plated and lubricated, with SAE J429 strength, the three-line head mark and the step down to 74 ksi above 1 in.
- Grade 8Grade 8 bolt torque from 1/4 in to 1 in, dry, zinc-plated and lubricated, with SAE J429 proof, yield and tensile strength and the six-line head marking.
- A325A325 bolts have no RCSC torque value. Minimum pretension is 28 kips for 3/4 in and 51 kips for 1 in; the torque is found daily on the job for each wrench.
- Bolt torque calculatorBolt torque calculator for SAE and metric bolts by size, thread, grade and lubrication, using T = K × D × F with the proof loads from SAE J429 and ISO 898-1.
- Dry vs lubricated torqueWhy oiled bolts need less torque than dry ones for the same clamp load, with nut factor K values from Fastenal, NASA and Henkel for oil, zinc, anti-seize and moly.