1/2 inch bolt torque specifications (Grade 2, 5, 8)
A 1/2-13 Grade 5 bolt takes 75 ft-lb (102 N·m) and a Grade 8 takes 107 ft-lb (144 N·m). Both values are for plain, dry steel threads (K 0.20) tightened to 75% of proof load.
Contents12 sections
Key takeaways
- Fastenal's own worked example, a 1/2-13 Grade 5 at K 0.20, gives the same 75 ft-lb 1.
- Oiled threads need 25% less torque for the same clamp load (K 0.15 vs 0.20) 1: 57 ft-lb for Grade 5, 80 ft-lb for Grade 8.
- 1/2-20 fine thread carries 12.7% more clamp load than 1/2-13 (10,200 against 9,050 lbf in Grade 5).
- Hex cap screw 3/4 in; structural heavy hex 7/8 in 1.
Quick facts
| Coarse thread | 1/2-13 UNC |
|---|---|
| Fine thread | 1/2-20 UNF |
| Wrench, hex cap screw and nut | 3/4 in |
| Wrench, heavy hex bolt | 7/8 in |
1/2 in bolt specifications
| Thread | Pitch | Tensile stress area |
|---|---|---|
| 1/2-13 (UNC) | 13 threads per inch | 0.1420 in² |
| 1/2-20 (UNF) | 20 threads per inch | 0.1600 in² |
| Wrench, hex cap screw | 3/4 in1 | |
| Wrench, heavy hex (structural) | 7/8 in | |
Stress areas from ASME B1.1 as tabulated by Fastenal1.
1/2 in torque by grade
| Grade | Plain, dry K 0.201 | Lubricated K 0.151 | Clamp load |
|---|---|---|---|
| Grade 2 | 49 ft-lb66 N·m | 37 ft-lb50 N·m | 5,860 lbf |
| Grade 5 | 75 ft-lb102 N·m | 57 ft-lb77 N·m | 9,050 lbf |
| Grade 8 | 107 ft-lb144 N·m | 80 ft-lb108 N·m | 12,780 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.
1/2 in Grade 2 torque
Proof 55,000 psi · yield 57,000 psi · tensile 74,000 psi1. Clamp load at 75% of proof: 5,860 lbf (1/2-13).
| Condition | K | 1/2-13 | 1/2-20 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 49 ft-lb66 N·m | 55 ft-lb75 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 44 ft-lb60 N·m | 50 ft-lb67 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 37 ft-lb50 N·m | 41 ft-lb56 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.163 | 39 ft-lb53 N·m | 44 ft-lb60 N·m |
| Moly pasteMolybdenum disulfide paste | 0.114 | 27 ft-lb36 N·m | 30 ft-lb41 N·m |
1/2 in Grade 5 torque
Proof 85,000 psi · yield 92,000 psi · tensile 120,000 psi1. Clamp load at 75% of proof: 9,050 lbf (1/2-13).
| Condition | K | 1/2-13 | 1/2-20 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 75 ft-lb102 N·m | 85 ft-lb115 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 68 ft-lb92 N·m | 77 ft-lb104 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 57 ft-lb77 N·m | 64 ft-lb86 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.163 | 60 ft-lb82 N·m | 68 ft-lb92 N·m |
| Moly pasteMolybdenum disulfide paste | 0.114 | 41 ft-lb56 N·m | 47 ft-lb63 N·m |
1/2 in Grade 8 torque
Proof 120,000 psi · yield 130,000 psi · tensile 150,000 psi1. Clamp load at 75% of proof: 12,780 lbf (1/2-13).
| Condition | K | 1/2-13 | 1/2-20 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 107 ft-lb144 N·m | 120 ft-lb163 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 96 ft-lb130 N·m | 108 ft-lb146 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 80 ft-lb108 N·m | 90 ft-lb122 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.163 | 85 ft-lb116 N·m | 96 ft-lb130 N·m |
| Moly pasteMolybdenum disulfide paste | 0.114 | 59 ft-lb79 N·m | 66 ft-lb89 N·m |
Coarse or fine thread
The 1/2-13 coarse thread has a tensile stress area of 0.142 in²; the 1/2-20 fine thread has 0.160 in² 1. The fine thread carries 12.7% more clamp load at the same stress, so its torque is higher by the same ratio: 85 ft-lb against 75 ft-lb in Grade 5 dry, 120 against 107 ft-lb in Grade 8. Read the column for the thread you have.
What clean, dry 1/2 in hardware really does
Henkel’s lubricant tests use 1/2 in Grade 8 bolts with Grade 5 nuts. Solvent-cleaned and unlubricated, that hardware measured K 0.27; with copper anti-seize it dropped to 0.16, and with moly paste to 0.11 3 4.
Two things follow. A degreased bolt can run well above the chart’s dry K of 0.20: at K 0.27, the 107 ft-lb Grade 8 value would give only about 74% of the intended 12,780 lbf. And moly is far more slippery than the oiled row: 107 ft-lb at K 0.11 would ask for about 1.8 times the chart clamp load, well past proof. Set the torque from the K that matches the threads; dry vs lubricated torque has the conversions.
Which grade you have
Grade 2 has a plain head, Grade 5 three radial lines and Grade 8 six 1. Proof stress is 55,000, 85,000 and 120,000 psi at this size 1, so Grade 8 takes 41% more torque than Grade 5 and Grade 5 55% more than Grade 2 (49 ft-lb dry). Grade 5 bolts take Grade 5 nuts and Grade 8 bolts Grade 8 nuts 1. See the grades page.
Structural bolts at 1/2 in
1/2 in is the smallest A325 and A490 heavy hex size 5. Those bolts are not installed from a torque chart. The RCSC requires a minimum pretension of 12 kips for A325 and 15 kips for A490 at 1/2 in 6, and for the calibrated-wrench method it forbids torque values taken from tables or equations without verification 6. For comparison, the Grade 5 chart value clamps 9,050 lbf. See A325 bolt torque.
When the chart does not apply
The chart sizes clamp load to the bolt’s proof load. It does not check whether the clamped parts or a tapped hole can take 9,000 to 14,000 lbf, and preload from a torque wrench scatters by about ±25% 2. When the equipment maker gives a torque, use the maker’s value.
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
- 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.
- 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.
- 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.
- 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.