5/16 inch bolt torque specifications (Grade 2, 5, 8)
A 5/16-18 Grade 5 bolt takes 17 ft-lb (24 N·m) and a Grade 8 takes 25 ft-lb (33 N·m). Both values are for plain, dry steel threads (K 0.20) tightened to 75% of proof load.
Contents11 sections
Key takeaways
- 5/16 is the first size where every grade reaches 10 ft-lb dry: Grade 2 is 11 ft-lb, Grade 5 is 17 ft-lb, Grade 8 is 25 ft-lb.
- Lubricated threads need 25% less torque for the same clamp load (K 0.15 vs 0.20) 1: 13 ft-lb for Grade 5.
- 5/16-24 fine thread carries 10.7% more clamp load than 5/16-18, the smallest gain of the sizes from 1/4 to 3/4 in.
- A 1/2 in wrench fits both the hex head and the hex nut 1.
Quick facts
| Coarse thread | 5/16-18 UNC |
|---|---|
| Fine thread | 5/16-24 UNF |
| Wrench (head and nut) | 1/2 in |
| Grade 8 clamp load, coarse | 4,720 lbf |
5/16 in bolt specifications
| Thread | Pitch | Tensile stress area |
|---|---|---|
| 5/16-18 (UNC) | 18 threads per inch | 0.0525 in² |
| 5/16-24 (UNF) | 24 threads per inch | 0.0581 in² |
| Wrench, hex cap screw | 1/2 in1 | |
Stress areas from ASME B1.1 as tabulated by Fastenal1.
5/16 in torque by grade
| Grade | Plain, dry K 0.201 | Lubricated K 0.151 | Clamp load |
|---|---|---|---|
| Grade 2 | 11 ft-lb15 N·m | 102 in-lb11 N·m | 2,170 lbf |
| Grade 5 | 17 ft-lb24 N·m | 13 ft-lb18 N·m | 3,350 lbf |
| Grade 8 | 25 ft-lb33 N·m | 18 ft-lb25 N·m | 4,730 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.
5/16 in Grade 2 torque
Proof 55,000 psi · yield 57,000 psi · tensile 74,000 psi1. Clamp load at 75% of proof: 2,170 lbf (5/16-18).
| Condition | K | 5/16-18 | 5/16-24 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 11 ft-lb15 N·m | 12 ft-lb17 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 10 ft-lb14 N·m | 11 ft-lb15 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 102 in-lb11 N·m | 112 in-lb13 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.163 | 108 in-lb12 N·m | 120 in-lb14 N·m |
| Moly pasteMolybdenum disulfide paste | 0.114 | 74 in-lb8.4 N·m | 82 in-lb9.3 N·m |
5/16 in Grade 5 torque
Proof 85,000 psi · yield 92,000 psi · tensile 120,000 psi1. Clamp load at 75% of proof: 3,350 lbf (5/16-18).
| Condition | K | 5/16-18 | 5/16-24 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 17 ft-lb24 N·m | 19 ft-lb26 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 16 ft-lb21 N·m | 17 ft-lb24 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 13 ft-lb18 N·m | 14 ft-lb20 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.163 | 14 ft-lb19 N·m | 15 ft-lb21 N·m |
| Moly pasteMolybdenum disulfide paste | 0.114 | 115 in-lb13 N·m | 11 ft-lb14 N·m |
5/16 in Grade 8 torque
Proof 120,000 psi · yield 130,000 psi · tensile 150,000 psi1. Clamp load at 75% of proof: 4,730 lbf (5/16-18).
| Condition | K | 5/16-18 | 5/16-24 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 25 ft-lb33 N·m | 27 ft-lb37 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 22 ft-lb30 N·m | 25 ft-lb33 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 18 ft-lb25 N·m | 20 ft-lb28 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.163 | 20 ft-lb27 N·m | 22 ft-lb30 N·m |
| Moly pasteMolybdenum disulfide paste | 0.114 | 14 ft-lb18 N·m | 15 ft-lb20 N·m |
Coarse or fine thread
The 5/16-18 coarse thread has a tensile stress area of 0.0525 in²; the 5/16-24 fine thread has 0.0581 in² 1. That is 10.7% more steel, so at the same grade the fine thread clamps 10.7% harder: 3,700 lbf against 3,350 lbf in Grade 5, and 19 ft-lb against 17 ft-lb dry. From 1/4 to 3/4 in that is the smallest coarse-to-fine difference; at 1/4 in it is 14.5%.
The 24 threads per inch of 5/16-24 is the same pitch as 3/8-24, so a thread gauge alone will not tell those two apart. Measure the diameter as well before you pick a column.
The coarse stress area printed here is Fastenal’s 0.0525 in²; the ASME B1.1 formula gives 0.0524 in² 5. The difference is under 0.2% and does not change any rounded torque on this page.
Which grade you have
Grade 2 heads carry no marking, Grade 5 shows three radial lines and Grade 8 six 1. At 5/16 in the proof stresses are 55,000, 85,000 and 120,000 psi 1. In practice:
- Grade 5 carries 55% more clamp load than Grade 2 (3,350 against 2,170 lbf).
- Grade 8 carries 41% more than Grade 5 (4,720 lbf).
- Torque scales the same way, so a Grade 8 value on a Grade 5 bolt asks 41% more of it than the chart intends.
Match the nut: a Grade 5 bolt takes a Grade 5 nut (Grade 8 may substitute) and a Grade 8 bolt a Grade 8 nut 1. Markings for every grade are on the grades page.
Dry, zinc or oiled
The three rows that matter most at this size differ only in K. Zinc-plated dry threads (K 0.18) need 16 ft-lb in Grade 5; oiled threads (K 0.15) need 13 ft-lb 1. Fastenal warns that an excessively lubricated zinc-plated bolt can drop to K 0.10 1, which would turn the 17 ft-lb dry figure into about twice the intended clamp load. Pick the row by what is actually on the threads; dry vs lubricated torque covers the other lubricants.
When the chart does not apply
The values are sized to the bolt’s proof load and assume the nut factor shown. They do not check whether the parts being clamped or a tapped hole can take 3,000 to 5,000 lbf of clamp, and NASA cautions that the usual K of 0.20 “should not be used blindly” 2. When the equipment maker gives a torque, use the maker’s value.
Sources
- 1
- 2
- 3
- 4Henkel Corporation (LOCTITE), LOCTITE LB 8012 Moly Paste TDS, April 2015Checked 21 Oct 2026
- 5
Spotted a value that doesn’t match its source? Report an error
Related
- 1/4 in1/4-20 Grade 5 bolt torque is 101 in-lb dry and Grade 8 is 12 ft-lb. Charts for 1/4-20 and 1/4-28 in Grade 2, 5 and 8, dry, zinc and oiled.
- 3/8 in3/8-16 Grade 5 bolt torque is 31 ft-lb dry and Grade 8 is 44 ft-lb. Charts for 3/8-16 and 3/8-24 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.
- 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.