5/8 inch bolt torque specifications (Grade 2, 5, 8)
A 5/8-11 Grade 5 bolt takes 150 ft-lb (203 N·m) and a Grade 8 takes 212 ft-lb (287 N·m). Both values are for plain, dry steel threads (K 0.20) tightened to 75% of proof load.
Contents11 sections
Key takeaways
- Oiled threads need 25% less torque for the same clamp load (K 0.15 vs 0.20) 1: 113 ft-lb for Grade 5, 159 ft-lb for Grade 8.
- 5/8-18 fine thread carries 13.3% more clamp load than 5/8-11 (16,320 against 14,410 lbf in Grade 5).
- Hex cap screw and nut 15/16 in; structural heavy hex 1-1/16 in 1.
- A325 structural bolts at 5/8 in need at least 19 kips of pretension 2, about a third more than the Grade 5 chart clamp.
Quick facts
| Coarse thread | 5/8-11 UNC |
|---|---|
| Fine thread | 5/8-18 UNF |
| Wrench, hex cap screw and nut | 15/16 in |
| Wrench, heavy hex bolt | 1-1/16 in |
5/8 in bolt specifications
| Thread | Pitch | Tensile stress area |
|---|---|---|
| 5/8-11 (UNC) | 11 threads per inch | 0.2260 in² |
| 5/8-18 (UNF) | 18 threads per inch | 0.2560 in² |
| Wrench, hex cap screw | 15/16 in1 | |
| Wrench, heavy hex (structural) | 1-1/16 in | |
Stress areas from ASME B1.1 as tabulated by Fastenal1.
5/8 in torque by grade
| Grade | Plain, dry K 0.201 | Lubricated K 0.151 | Clamp load |
|---|---|---|---|
| Grade 2 | 97 ft-lb132 N·m | 73 ft-lb99 N·m | 9,320 lbf |
| Grade 5 | 150 ft-lb203 N·m | 113 ft-lb153 N·m | 14,410 lbf |
| Grade 8 | 212 ft-lb287 N·m | 159 ft-lb215 N·m | 20,340 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%3. When the equipment maker gives a torque, use theirs. How these numbers are made.
5/8 in Grade 2 torque
Proof 55,000 psi · yield 57,000 psi · tensile 74,000 psi1. Clamp load at 75% of proof: 9,320 lbf (5/8-11).
| Condition | K | 5/8-11 | 5/8-18 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 97 ft-lb132 N·m | 110 ft-lb149 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 87 ft-lb118 N·m | 99 ft-lb134 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 73 ft-lb99 N·m | 83 ft-lb112 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.164 | 78 ft-lb105 N·m | 88 ft-lb119 N·m |
| Moly pasteMolybdenum disulfide paste | 0.115 | 53 ft-lb72 N·m | 61 ft-lb82 N·m |
5/8 in Grade 5 torque
Proof 85,000 psi · yield 92,000 psi · tensile 120,000 psi1. Clamp load at 75% of proof: 14,410 lbf (5/8-11).
| Condition | K | 5/8-11 | 5/8-18 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 150 ft-lb203 N·m | 170 ft-lb230 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 135 ft-lb183 N·m | 153 ft-lb207 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 113 ft-lb153 N·m | 128 ft-lb173 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.164 | 120 ft-lb163 N·m | 136 ft-lb184 N·m |
| Moly pasteMolybdenum disulfide paste | 0.115 | 83 ft-lb112 N·m | 94 ft-lb127 N·m |
5/8 in Grade 8 torque
Proof 120,000 psi · yield 130,000 psi · tensile 150,000 psi1. Clamp load at 75% of proof: 20,340 lbf (5/8-11).
| Condition | K | 5/8-11 | 5/8-18 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 212 ft-lb287 N·m | 240 ft-lb325 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 191 ft-lb259 N·m | 216 ft-lb293 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 159 ft-lb215 N·m | 180 ft-lb244 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.164 | 170 ft-lb230 N·m | 192 ft-lb260 N·m |
| Moly pasteMolybdenum disulfide paste | 0.115 | 117 ft-lb158 N·m | 132 ft-lb179 N·m |
Coarse or fine thread
The 5/8-11 coarse thread has a tensile stress area of 0.226 in²; the 5/8-18 fine thread has 0.256 in² 1. That 13.3% gain is the largest of the sizes from 1/2 to 1 in. At the same grade, 5/8-18 needs 170 ft-lb against 150 ft-lb in Grade 5 dry, and 240 against 212 ft-lb in Grade 8.
Which grade you have
Grade 2 heads are plain, Grade 5 heads carry three radial lines and Grade 8 six 1. Proof stress at 5/8 in is 55,000, 85,000 and 120,000 psi 1. The torque gaps are wide in absolute terms at this size: 97 ft-lb for Grade 2, 150 for Grade 5 and 212 for Grade 8, all dry. Torquing an unmarked bolt to the Grade 5 value asks 55% more of it than the chart intends. Match the nut: Grade 5 nut on a Grade 5 bolt, Grade 8 nut on a Grade 8 bolt 1. The grades page shows the markings.
Structural bolts at 5/8 in
A325 and A490 heavy hex bolts at 5/8 in are installed to an RCSC minimum pretension, not a chart torque: 19 kips for A325 and 24 kips for A490 2. Those figures sit above the Grade 5 chart clamp of 14,410 lbf and, for A490, above the Grade 8 chart clamp of 20,340 lbf. For the calibrated-wrench method RCSC forbids torque values taken from tables or equations without verification 2.
For galvanized joints RCSC cites a pretension loss of about 6.5% within five days for galvanized plates and bolts, against 2.5% uncoated 2. See A325 bolt torque and A490 bolt torque.
When the chart does not apply
The values size clamp load to the bolt’s proof load with the K shown in each row. They do not check whether the clamped parts or a tapped hole can carry 9,000 to 23,000 lbf, and preload from a torque wrench scatters by about ±25% 3. When the equipment maker gives a torque, use the maker’s value. For greased or anti-seized threads see dry vs lubricated torque.
Sources
- 1
- 2
- 3
- 4
- 5Henkel Corporation (LOCTITE), LOCTITE LB 8012 Moly Paste TDS, April 2015Checked 21 Oct 2026
Spotted a value that doesn’t match its source? Report an error
Related
- 9/16 in9/16-12 Grade 5 bolt torque is 109 ft-lb dry and Grade 8 is 154 ft-lb. Charts for 9/16-12 and 9/16-18 in Grade 2, 5 and 8, dry, zinc-plated and oiled.
- 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.
- 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.
- 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.
- 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.
- A490A490 bolts have no RCSC torque value. Minimum pretension is 35 kips for 3/4 in and 64 kips for 1 in; RCSC bans galvanizing and reuse of A490 heavy hex bolts.
- 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.