3/8 inch bolt torque specifications (Grade 2, 5, 8)
A 3/8-16 Grade 5 bolt takes 31 ft-lb (42 N·m) and a Grade 8 takes 44 ft-lb (59 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: 23 ft-lb for Grade 5, 33 ft-lb for Grade 8.
- 3/8-24 fine thread carries 13.3% more clamp load than 3/8-16 (5,600 against 4,940 lbf in Grade 5).
- Henkel measured its marine and silver anti-seize at K 0.18 on 3/8-16 steel bolts 2 3, closer to the zinc row than the oiled row.
- A 9/16 in wrench fits both the hex head and the hex nut 1.
Quick facts
| Coarse thread | 3/8-16 UNC |
|---|---|
| Fine thread | 3/8-24 UNF |
| Wrench (head and nut) | 9/16 in |
| Grade 5 clamp load, coarse | 4,940 lbf |
3/8 in bolt specifications
| Thread | Pitch | Tensile stress area |
|---|---|---|
| 3/8-16 (UNC) | 16 threads per inch | 0.0775 in² |
| 3/8-24 (UNF) | 24 threads per inch | 0.0878 in² |
| Wrench, hex cap screw | 9/16 in1 | |
Stress areas from ASME B1.1 as tabulated by Fastenal1.
3/8 in torque by grade
| Grade | Plain, dry K 0.201 | Lubricated K 0.151 | Clamp load |
|---|---|---|---|
| Grade 2 | 20 ft-lb27 N·m | 15 ft-lb20 N·m | 3,200 lbf |
| Grade 5 | 31 ft-lb42 N·m | 23 ft-lb31 N·m | 4,940 lbf |
| Grade 8 | 44 ft-lb59 N·m | 33 ft-lb44 N·m | 6,980 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%4. When the equipment maker gives a torque, use theirs. How these numbers are made.
3/8 in Grade 2 torque
Proof 55,000 psi · yield 57,000 psi · tensile 74,000 psi1. Clamp load at 75% of proof: 3,200 lbf (3/8-16).
| Condition | K | 3/8-16 | 3/8-24 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 20 ft-lb27 N·m | 23 ft-lb31 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 18 ft-lb24 N·m | 20 ft-lb28 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 15 ft-lb20 N·m | 17 ft-lb23 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.165 | 16 ft-lb22 N·m | 18 ft-lb25 N·m |
| Moly pasteMolybdenum disulfide paste | 0.116 | 11 ft-lb15 N·m | 12 ft-lb17 N·m |
3/8 in Grade 5 torque
Proof 85,000 psi · yield 92,000 psi · tensile 120,000 psi1. Clamp load at 75% of proof: 4,940 lbf (3/8-16).
| Condition | K | 3/8-16 | 3/8-24 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 31 ft-lb42 N·m | 35 ft-lb47 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 28 ft-lb38 N·m | 31 ft-lb43 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 23 ft-lb31 N·m | 26 ft-lb36 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.165 | 25 ft-lb33 N·m | 28 ft-lb38 N·m |
| Moly pasteMolybdenum disulfide paste | 0.116 | 17 ft-lb23 N·m | 19 ft-lb26 N·m |
3/8 in Grade 8 torque
Proof 120,000 psi · yield 130,000 psi · tensile 150,000 psi1. Clamp load at 75% of proof: 6,980 lbf (3/8-16).
| Condition | K | 3/8-16 | 3/8-24 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 44 ft-lb59 N·m | 49 ft-lb67 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 39 ft-lb53 N·m | 44 ft-lb60 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 33 ft-lb44 N·m | 37 ft-lb50 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.165 | 35 ft-lb47 N·m | 40 ft-lb54 N·m |
| Moly pasteMolybdenum disulfide paste | 0.116 | 24 ft-lb33 N·m | 27 ft-lb37 N·m |
Coarse or fine thread
The 3/8-16 coarse thread has a tensile stress area of 0.0775 in²; the 3/8-24 fine thread has 0.0878 in² 1. That 13.3% extra steel is matched only by 5/8 in among the sizes from 5/16 to 1 in; 7/16 in, for comparison, gains 12.3%. At the same grade, 3/8-24 clamps 13.3% harder and the calculated torque rises by the same ratio: 35 ft-lb against 31 ft-lb in Grade 5 dry.
3/8-24 shares its 24 threads per inch with 5/16-24, so check the diameter as well as the pitch before choosing a column.
What the lubricant tests at 3/8-16 show
Several manufacturer nut-factor tests use 3/8-16 steel hardware, which makes this size a useful check on the chart rows:
- LOCTITE 242 threadlocker: K within ±10% of the same hardware unlubricated 7. Henkel adds that critical joints need their own K test 7.
- LOCTITE marine-grade anti-seize: K 0.18 2.
- LOCTITE silver-grade anti-seize stick: K 0.18 3.
At K 0.18 a 3/8-16 Grade 5 needs 28 ft-lb for the chart’s 4,940 lbf, the same as the zinc-plated row. Using the oiled figure (23 ft-lb) with those compounds would leave about 17% less clamp load than intended. The anti-seize and thread locker guides cover other products.
Which grade you have
No head marking means Grade 2, three radial lines Grade 5, six radial lines Grade 8 1. Proof stress at 3/8 in is 55,000, 85,000 and 120,000 psi 1, so Grade 8 takes 41% more torque than Grade 5 (44 against 31 ft-lb dry), and Grade 5 takes 55% more than Grade 2 (20 ft-lb). Fit a Grade 5 nut to a Grade 5 bolt and a Grade 8 nut to a Grade 8 bolt 1. See the grades page for the markings.
When the chart does not apply
The chart sizes clamp load to the bolt’s proof load with the K values shown. It does not check whether the clamped parts or a tapped hole can carry about 5,000 to 7,000 lbf, and preload from a torque wrench scatters by about ±25% even when the K is right 4. When the equipment maker gives a torque, use the maker’s value.
Sources
- 1
- 2
- 3
- 4
- 5
- 6Henkel Corporation (LOCTITE), LOCTITE LB 8012 Moly Paste TDS, April 2015Checked 21 Oct 2026
- 7Henkel Corporation (LOCTITE), LOCTITE 242 threadlocker TDS, February 2022Checked 21 Oct 2026
Spotted a value that doesn’t match its source? Report an error
Related
- 5/16 in5/16-18 Grade 5 bolt torque is 17 ft-lb dry and Grade 8 is 25 ft-lb. Charts for 5/16-18 and 5/16-24 in Grade 2, 5 and 8, dry, zinc-plated and oiled.
- 7/16 in7/16-14 Grade 5 bolt torque is 49 ft-lb dry and Grade 8 is 70 ft-lb. Charts for 7/16-14 and 7/16-20 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.
- Anti-seize torqueHow much to cut torque with anti-seize, from LOCTITE data sheets: copper and metal-free K 0.16, marine and silver 0.18, moly 0.11. And why NGK says no on plugs.
- Thread locker torqueLOCTITE 242 changes the nut factor by no more than ±10%, so torque stays at the dry value. Henkel publishes no figure for 243, 262 or 271. What the data sheets do say.