M3 bolt torque specifications (8.8, 10.9, 12.9)
An M3 x 0.5 class 8.8 screw takes 12 in-lb (1.3 N·m) dry, and class 10.9 takes 17 in-lb (1.9 N·m). Both are for plain steel, dry threads (K 0.20) tightened to a clamp load of 75% of proof load.
Contents13 sections
Key takeaways
- Class 8.8 dry: 12 in-lb (1.3 N·m), under 1 ft-lb, so read it on an in-lb scale.
- Class 10.9 dry: 17 in-lb (1.9 N·m); 12.9 dry: 19 in-lb (2.2 N·m).
- Oiled 8.8 drops to 9 in-lb (1.0 N·m); the dry figure on an oiled screw overshoots the clamp target by about a third.
- M4 needs about 2.3 times the M3 torque in the same class.
Quick facts
| Coarse thread | M3 x 0.5 (5.03 mm²) |
|---|---|
| Fine thread | M3 x 0.35 (5.6 mm²) |
| Wrench, ISO 4014/4017 | 5.5 mm |
| Wrench, DIN 931/933 | 5.5 mm (same) |
M3 bolt specifications
| Thread | Pitch | Tensile stress area |
|---|---|---|
| M3 x 0.5 (coarse) | 0.5 mm pitch | 5.0 mm² |
| M3 x 0.35 (fine) | 0.35 mm pitch | 5.6 mm² |
| Wrench, ISO 4014/4017 | 5.5 mm1 | |
Stress areas from ISO 898-1 Table 42.
M3 torque by grade
| Grade | Plain, dry K 0.201 | Lubricated K 0.151 | Clamp load |
|---|---|---|---|
| Class 4.6 | 5 in-lb0.5 N·m | 3 in-lb0.4 N·m | 0.8 kN |
| Class 8.8 | 12 in-lb1.3 N·m | 9 in-lb1.0 N·m | 2.2 kN |
| Class 10.9 | 17 in-lb1.9 N·m | 12 in-lb1.4 N·m | 3.1 kN |
| Class 12.9 | 19 in-lb2.2 N·m | 15 in-lb1.6 N·m | 3.7 kN |
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.
M3 4.6 torque
Proof 225 MPa · yield 240 MPa · tensile 400 MPa2. Clamp load at 75% of proof: 0.8 kN (M3 x 0.5).
| Condition | K | M3 x 0.5 | M3 x 0.35 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 5 in-lb0.5 N·m | 5 in-lb0.6 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 4 in-lb0.5 N·m | 5 in-lb0.5 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 3 in-lb0.4 N·m | 4 in-lb0.4 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.164 | 4 in-lb0.4 N·m | 4 in-lb0.5 N·m |
| Moly pasteMolybdenum disulfide paste | 0.115 | 2 in-lb0.3 N·m | 3 in-lb0.3 N·m |
M3 8.8 torque
Proof 580 MPa · yield 640 MPa · tensile 800 MPa2. Clamp load at 75% of proof: 2.2 kN (M3 x 0.5).
| Condition | K | M3 x 0.5 | M3 x 0.35 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 12 in-lb1.3 N·m | 13 in-lb1.5 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 10 in-lb1.2 N·m | 12 in-lb1.3 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 9 in-lb1.0 N·m | 10 in-lb1.1 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.164 | 9 in-lb1.1 N·m | 10 in-lb1.2 N·m |
| Moly pasteMolybdenum disulfide paste | 0.115 | 6 in-lb0.7 N·m | 7 in-lb0.8 N·m |
M3 10.9 torque
Proof 830 MPa · yield 940 MPa · tensile 1040 MPa2. Clamp load at 75% of proof: 3.1 kN (M3 x 0.5).
| Condition | K | M3 x 0.5 | M3 x 0.35 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 17 in-lb1.9 N·m | 19 in-lb2.1 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 15 in-lb1.7 N·m | 17 in-lb1.9 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 12 in-lb1.4 N·m | 14 in-lb1.6 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.164 | 13 in-lb1.5 N·m | 15 in-lb1.7 N·m |
| Moly pasteMolybdenum disulfide paste | 0.115 | 9 in-lb1.0 N·m | 10 in-lb1.2 N·m |
M3 12.9 torque
Proof 970 MPa · yield 1100 MPa · tensile 1220 MPa2. Clamp load at 75% of proof: 3.7 kN (M3 x 0.5).
| Condition | K | M3 x 0.5 | M3 x 0.35 |
|---|---|---|---|
| Plain steel, dryAs-received black or plain finish, clean threads, no lubricant | 0.201 | 19 in-lb2.2 N·m | 22 in-lb2.4 N·m |
| Zinc-plated, dryClean zinc-plated threads, no added lubricant | 0.181 | 17 in-lb2.0 N·m | 19 in-lb2.2 N·m |
| Lubricated (oil or grease)Light oil or grease on the threads and under the nut or head | 0.151 | 15 in-lb1.6 N·m | 16 in-lb1.8 N·m |
| Copper or metal-free anti-seizeLoctite C5-A copper or N-7000 metal-free anti-seize | 0.164 | 16 in-lb1.8 N·m | 17 in-lb2.0 N·m |
| Moly pasteMolybdenum disulfide paste | 0.115 | 11 in-lb1.2 N·m | 12 in-lb1.3 N·m |
Coarse or fine pitch
The tables use M3 x 0.5 coarse, with a tensile stress area of 5.03 mm² 2. The fine pitch, M3 x 0.35, is listed in the ISO 262 selected-sizes table 6; its 5.6 mm² stress area is about 11% larger. At the same 75%-of-proof target, the fine thread carries about 11% more clamp load and needs about 11% more torque. In class 8.8 dry that is 13 in-lb instead of 12 in-lb, a difference the whole-in-lb rounding mostly hides.
Reading torque this small
Class 8.8 dry works out to 0.97 ft-lb, which is why the chart gives 12 in-lb (1.3 N·m). The clamp load behind it is 2.2 kN, about 490 lbf; class 10.9 raises that to 3.1 kN, about 700 lbf.
Tightening with a torque wrench scatters preload by about ±25% 3. On an M3 class 8.8 that means 12 in-lb can leave anywhere from about 1.6 to 2.7 kN in the screw.
One size up, M4 x 0.7 has 1.75 times the stress area and a larger diameter, so it needs 2.3 times the torque in the same class: 27 in-lb for 8.8 dry. Picking the M4 number for an M3 screw would load it well past proof.
Wrench size
A hex-head M3 takes a 5.5 mm wrench under both ISO 4014/4017 and the older DIN 931/933 1. The two standards first give different wrench sizes at M10.
Which class you have
ISO 898-1 calls for the property class symbol and the maker’s mark on the head 2; see bolt grade markings. The number before the dot is the nominal tensile strength in hundreds of MPa, and the number after it is ten times the yield-to-tensile ratio 2. Going from 8.8 to 10.9 takes the M3 dry torque from 12 to 17 in-lb; 12.9 reaches 19 in-lb. Class 9.8, which ISO 898-1 defines only up to M16 2, is not in these tables.
When the chart does not apply
The dry figures assume plain steel with no lubricant (K 0.20) 1. A lightly oiled M3 class 8.8 is 9 in-lb (1.0 N·m) at K 0.15 1; putting the 12 in-lb dry value on an oiled screw raises the clamp load by about 33%, past the 75% target. See dry vs lubricated torque. When the maker of the part publishes a torque for the screw, use it instead of this chart.
Sources
- 1
- 2
- 3
- 4
- 5Henkel Corporation (LOCTITE), LOCTITE LB 8012 Moly Paste TDS, April 2015Checked 21 Oct 2026
- 6Wikipedia, Wikipedia: ISO metric screw thread (ISO 262 selected sizes table)Checked 21 Oct 2026
Spotted a value that doesn’t match its source? Report an error
Related
- M4M4 x 0.7 screw torque: 27 in-lb (3.1 N·m) for class 8.8 and 39 in-lb (4.4 N·m) for 10.9 dry, with 12.9, M4 x 0.5 fine, zinc and oiled values.
- Class 8.8Class 8.8 bolt torque from M3 to M30, dry, zinc-plated and lubricated, with the ISO 898-1 proof stress step from 580 MPa to 600 MPa above M16.
- Class 10.9Class 10.9 bolt torque from M3 to M30, dry, zinc-plated and lubricated, with ISO 898-1 strength (830 MPa proof) and how it compares with 8.8 and 12.9.
- Class 12.9Class 12.9 bolt torque from M3 to M30, dry, zinc-plated and lubricated, with ISO 898-1 strength (970 MPa proof, 1,220 MPa tensile) and nut matching notes.
- 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.