Guides and tools
Look up a size, estimate a torque, match a spanner or check a bolt grade. Then send us your list for a quote.
Size finder
Choose a thread size, or see the full size chart.
Dimensions in mm. Coarse pitch. Cap screw per ISO 4762, hex bolt per ISO 4017, hex nut style 1 per ISO 4032, clearance hole medium series per ISO 273.
Tightening torque estimator
Pick the bolt size, grade and thread condition to get a starting torque for a reusable joint.
Estimates for reusable joints: preload is 75% of proof (yield) load on the tensile stress area, torque T = K x preload x diameter. K is 0.20 for dry or plain threads and 0.15 for lightly oiled threads. Real joints vary with finish, washers and surface, so use the manufacturer's figure for critical joints.
Which size fits my spanner or key?
Know the spanner or hex key size but not the bolt? Pick it to see what it fits.
ISO sizes shown. Parts made to the older DIN standard often use a larger spanner: 17 mm for M10, 19 mm for M12 and 22 mm for M14.
Bolt grade guide
The first number times 100 is the minimum tensile strength in MPa. The second number is the yield-to-tensile ratio, as a tenth.
| Grade | Min. tensile (MPa) | Yield (MPa) | Typical use |
|---|---|---|---|
| 4.6 | 400 | 240 | Light-duty, non-critical fixing in mild steel. |
| 8.8 | 800 | 640 | General engineering and structural connections. The most common grade. |
| 10.9 | 1000 | 900 | High-strength joints in machinery and automotive assemblies. |
| 12.9 | 1200 | 1080 | Highest strength, typical for socket head cap screws in tooling and dies. |
| A2-70 | 700 | 450 | Stainless steel (304 type) for corrosion resistance. |
| A4-80 | 800 | 600 | Stainless steel (316 type) for harsher or marine environments. |
| Nut class | Use with |
|---|---|
| Class 8 | Bolt grades up to 8.8 |
| Class 10 | Bolt grade 10.9 |
| Class 12 | Bolt grade 12.9 |
Values are nominal minimums for common sizes. Check the relevant standard for the exact figure at a given diameter.
Grade questions
What do the two numbers in a grade like 8.8 mean?
The first number multiplied by 100 is the minimum tensile strength in MPa. The second number is the ratio of yield to tensile strength, so 8.8 means 800 MPa tensile and a yield of 0.8 times that, 640 MPa.
Can I use a lower-grade nut with a high-grade bolt?
It is not recommended. The nut should be of equal or higher property class than the bolt so the thread does not strip before the bolt reaches its rated load.
Is stainless steel stronger than 8.8?
No. A2-70 stainless has a minimum tensile strength of 700 MPa, below 8.8. Stainless is chosen for corrosion resistance, not strength.
Guides
- How to measure a bolt before you orderDiameter, thread pitch, length and head type. Four quick measurements that get you the right bolt the first time.2026-11-01
- How to read bolt grades (4.6, 8.8, 10.9, 12.9)What the numbers stamped on a bolt head mean, and how to choose the right property class for your job.2026-11-01
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