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Technical & standard
Find a size and its dimensions, check threads, grades and markings, work out torque and weight, then check coatings and corrosion.
Fastener standards & calculators
Find a size and its dimensions to DIN, ISO, IS and NF E, check threads, grades and markings, work out torque and weight, then check coatings and corrosion.
Bolt finder
Pick a metric size to see everything about it at once.
Fastener dimensions to DIN, ISO, IS and NF E
93 fastener types covering the standards on our DIN chart: bolts and machine screws, tapping and wood screws, studs, eye bolts, nuts, washers, pins, circlips, rivets, threaded rod and the French NF E standard fasteners (hex bolts, hex nuts, heavy flange bolts, Z / M / L / LL plain washers, CS and CL conical washers). Where DIN, ISO, IS and NF E differ, each standard has its own tab and the values that change are shaded, so you can see at a glance which sizes are not interchangeable. Click any row to update the drawing.
For information only. Values are nominal, taken from the standards as published (checked October 2026). Standards are revised: always check the current edition named on your drawing before production or inspection.
Thread, drill and clearance hole chart
Metric ISO threads. Clearance holes per ISO 273: fine for accurate location, medium for general use, coarse for site work.
| Thread | Coarse pitch | Fine pitch | Tapping drill | Clearance fine | Clearance medium | Clearance coarse | Spanner ISO (DIN) | Allen key (cap screw) |
|---|---|---|---|---|---|---|---|---|
| M3 | 0.5 | 0.35 | 2.5 | 3.2 | 3.4 | 3.6 | 5.5 | 2.5 |
| M4 | 0.7 | 0.5 | 3.3 | 4.3 | 4.5 | 4.8 | 7 | 3 |
| M5 | 0.8 | 0.5 | 4.2 | 5.3 | 5.5 | 5.8 | 8 | 4 |
| M6 | 1.0 | 0.75 | 5.0 | 6.4 | 6.6 | 7.0 | 10 | 5 |
| M8 | 1.25 | 1.0 | 6.8 | 8.4 | 9.0 | 10.0 | 13 | 6 |
| M10 | 1.5 | 1.25 / 1.0 | 8.5 | 10.5 | 11.0 | 12.0 | 16 (17) | 8 |
| M12 | 1.75 | 1.5 / 1.25 | 10.2 | 13.0 | 13.5 | 14.5 | 18 (19) | 10 |
| M14 | 2.0 | 1.5 | 12.0 | 15.0 | 15.5 | 16.5 | 21 (22) | 12 |
| M16 | 2.0 | 1.5 | 14.0 | 17.0 | 17.5 | 18.5 | 24 | 14 |
| M18 | 2.5 | 1.5 | 15.5 | 19.0 | 20.0 | 21.0 | 27 | 14 |
| M20 | 2.5 | 1.5 | 17.5 | 21.0 | 22.0 | 24.0 | 30 | 17 |
| M22 | 2.5 | 1.5 | 19.5 | 23.0 | 24.0 | 26.0 | 34 (32) | 17 |
| M24 | 3.0 | 2.0 | 21.0 | 25.0 | 26.0 | 28.0 | 36 | 19 |
| M27 | 3.0 | 2.0 | 24.0 | 28.0 | 30.0 | 32.0 | 41 | 19 |
| M30 | 3.5 | 2.0 | 26.5 | 31.0 | 33.0 | 35.0 | 46 | 22 |
| M36 | 4.0 | 3.0 | 32.0 | 37.0 | 39.0 | 42.0 | 55 | 27 |
Inch (UNC / UNF) sizes and nearest metric
For imported machinery and US drawings. Do not mix inch and metric threads: they may start but will strip.
| Size | Diameter (mm) | UNC (TPI) | UNF (TPI) | Nearest metric | Spanner (in) |
|---|---|---|---|---|---|
| #10 | 4.83 | 24 | 32 | M5 | 5/16 head · 3/8 nut |
| 1/4" | 6.35 | 20 | 28 | M6 | 7/16 |
| 5/16" | 7.94 | 18 | 24 | M8 | 1/2 |
| 3/8" | 9.53 | 16 | 24 | M10 | 9/16 |
| 7/16" | 11.11 | 14 | 20 | M11 / M12 | 5/8 |
| 1/2" | 12.70 | 13 | 20 | M12 | 3/4 |
| 5/8" | 15.88 | 11 | 18 | M16 | 15/16 |
| 3/4" | 19.05 | 10 | 16 | M20 | 1-1/8 |
| 7/8" | 22.23 | 9 | 14 | M22 | 1-5/16 |
| 1" | 25.40 | 8 | 12 (14 UNS) | M24 | 1-1/2 |
Property classes: steel bolts and nuts
ISO 898-1 (IS 1367 Part 3 in India). Read the class as two numbers: the first × 100 is the nominal tensile strength in MPa, and the second ÷ 10 is the yield-to-tensile ratio. A 10.9 bolt: nominal 1000 MPa tensile and 900 MPa yield; the guaranteed minimums in the table are a little higher (1040 / 940 MPa).
| Class | Min. tensile (MPa) | Min. yield / 0.2% proof (MPa) | Proof stress (MPa) | Core hardness | Matching nut | Typical use |
|---|---|---|---|---|---|---|
| 4.6 | 400 | 240 | 225 | 67–95 HRB | Class 5 (4 above M16) | Light fabrication, non-critical |
| 5.6 | 500 | 300 | 280 | 79–95 HRB | Class 5 | General fabrication |
| 8.8 (≤ M16) | 800 | 640 | 580 | 22–32 HRC | Class 8 | Structural and general engineering |
| 8.8 (> M16) | 830 | 660 | 600 | 23–34 HRC | Class 8 | Structural and general engineering |
| 10.9 | 1040 | 940 | 830 | 32–39 HRC | Class 10 | Machinery, automotive, high-load joints |
| 12.9 | 1220 | 1100 | 970 | 39–44 HRC | Class 12 | Socket cap screws, dies and tooling |
Rule: always use a nut of the same or higher class than the bolt. A weaker nut strips before the bolt reaches its strength.
Reading head markings
Metric steel bolts from M5 up carry the class and the maker's mark on the head. Stainless shows the grade. Inch (SAE) bolts use radial lines instead of numbers.
Stainless steel grades
ISO 3506-1. The letter and digit give the steel group, the number after the dash × 10 gives the minimum tensile strength in MPa.
| Grade | Steel | Min. tensile (MPa) | Min. 0.2% proof (MPa) | Corrosion | Where to use |
|---|---|---|---|---|---|
| A1-70 | 303 (free machining) | 700 | 450 | Fair | Indoor, dry |
| A2-70 | 304 | 700 | 450 | Good | General outdoor, food machinery, buildings |
| A4-70 | 316 | 700 | 450 | Very good | Coastal, marine, chemical and pharma |
| A4-80 | 316 | 800 | 600 | Very good | Stronger marine and chemical joints |
| C1-70 | 410 (martensitic) | 700 | 410 | Fair | Hardened self-drilling screws |
| Duplex 2205, class 80 | 1.4462 | 800 | 600 | Excellent | Offshore, desalination, high chlorides |
Quick choice: dry indoors, A2 is enough. Near the sea, swimming pools or chemicals, use A4. Stainless threads can gall; use anti-seize on A2 / A4 nuts and bolts.
ASTM studs and nuts for pressure service
Common pairings for flanges, valves and pressure vessels.
| Stud | Material | Min. tensile | Matching nut | Service |
|---|---|---|---|---|
| A193 B7 | Cr-Mo alloy steel | 125 ksi (860 MPa), up to 2½" | A194 2H | High temperature and pressure |
| A193 B7M | Cr-Mo, hardness-limited | 100 ksi (690 MPa) | A194 2HM | Sour (H₂S) service, NACE MR0175 |
| A193 B16 | Cr-Mo-V alloy steel | 125 ksi (860 MPa), up to 2½" | A194 4 / 7 | Higher temperature than B7 |
| A193 B8 / B8M | SS 304 / SS 316 | 75 ksi (515 MPa), class 1 | A194 8 / 8M | Corrosive service |
| A320 L7 | Cr-Mo alloy steel | 125 ksi (860 MPa), up to 2½" | A194 4 / 7 | Low temperature, down to −101 °C |
| A453 660 | A286 superalloy | 130 ksi (895 MPa) | A453 660 | Very high temperature |
Hardness conversion (approximate)
Useful when a drawing and a test certificate use different scales. Values per ASTM E140 tables, rounded.
| Rockwell C (HRC) | Rockwell B (HRB) | Vickers (HV) | Brinell (HB) | Approx. tensile (MPa) |
|---|---|---|---|---|
| — | 60 | 110 | 107 | ~370 |
| — | 70 | 125 | 122 | ~420 |
| — | 80 | 150 | 145 | ~500 |
| — | 90 | 185 | 176 | ~600 |
| 20 | ~98 | 238 | 226 | ~770 |
| 25 | — | 266 | 253 | ~860 |
| 30 | — | 302 | 286 | ~960 |
| 35 | — | 345 | 327 | ~1110 |
| 40 | — | 392 | 371 | ~1250 |
| 45 | — | 446 | 421 | ~1450 |
| 50 | — | 513 | 481 | ~1700 |
Tightening torque calculator
Preload is set to 75% of the proof load (ISO 898-1 proof stress for steel, 0.2% proof stress for stainless). Torque = K × preload × diameter.
For guidance only. Follow the torque given on your drawing or by the equipment maker, and use a calibrated torque wrench.
Fastener weight calculator
Choose any DIN, ISO, IS or NF E standard, then the size, length and material, to get the weight per piece, per 100 and per 1000, and how many pieces make a kilo. Useful for quotes, dispatch and freight.
- Standard table the mass published for that standard (kg per 1000 pcs, steel 7.85 g/cm³), for 46 standards including DIN 931, 933, 912, 934, 985, 125, 9021, 127, 7991, 7985, 965, 913, 916, 7984, 6912, 603, 6921, 84, 7, 1481, 471, 472, 975, 580 and 582. Between two listed lengths the value is interpolated; beyond the longest listed length it is extended at the table’s own weight per mm.
- Table-corrected no table for this exact standard or length: calculated from its own dimensions, then corrected with the published table of the same part (for example ISO 4014 with DIN 931, ISO 4032 with DIN 934). Typically within ±2–3 %.
- Calculated no published table exists: calculated from the standard’s dimensions, with the tolerance shown.
Sheet metal fasteners: holes and sheet hardness
Self-clinching parts must be harder than the sheet. Blind rivets and rivet nuts need the right hole: too small and they will not enter, too big and they spin.
| Sheet | Typical hardness | Clinch fastener to use |
|---|---|---|
| Aluminium | HRB ≤ 50 | Aluminium, steel or stainless clinch fasteners |
| Mild steel / CRCA | HRB ≤ 70–80 | Steel or stainless clinch fasteners |
| Stainless 304 / 316 | HRB ≤ 88–92 | Hardened 400-series or A286 clinch fasteners |
| Size | Blind rivet hole | Rivet nut thread | Rivet nut hole (round) |
|---|---|---|---|
| 2.4 mm | 2.5 | M3 | 5.0 |
| 3.2 mm | 3.3 | M4 | 6.0 |
| 4.0 mm | 4.1 | M5 | 7.0 |
| 4.8 mm | 4.9 | M6 | 9.0 |
| 6.4 mm | 6.5 | M8 | 11.0 |
| — | — | M10 | 13.0 |
| — | — | M12 | 15.0 / 16.0 |
Coatings and finishes
Choose a finish by where the joint will live. Salt-spray hours are typical values to red rust and depend on the exact specification.
| Finish | Thickness | Salt spray (typical) | Best for | Watch out for |
|---|---|---|---|---|
| Zinc plated, clear / blue | 5–8 µm | 72–120 h | Indoors, dry outdoor | Rusts quickly near the sea |
| Zinc plated, yellow | 8 µm | 96–200 h | Machinery, electrical panels | Usually hexavalent chromium: not RoHS compliant |
| Zinc-nickel | 8–12 µm | 500–720 h+ | Automotive, under-bonnet | Higher cost |
| Hot-dip galvanised (HDG) | 45–85 µm | Decades outdoors | Structures, towers, outdoor steel | Nuts are tapped oversize; use HDG nuts |
| Zinc flake (Geomet, Delta-Protekt) | 8–12 µm | 480–1000 h | 10.9 / 12.9 bolts, wind, automotive | No hydrogen embrittlement risk |
| Black oxide + oil | ~1 µm | Very low | Socket cap screws indoors, tooling | Not for outdoor use |
| Phosphate + oil | 5–15 µm | Low | Lubricated assembly, paint base | Store dry |
| Stainless, passivated | — | Inherent | Food, marine, chemical | Galling; isolate from aluminium in wet areas |
Electroplating 10.9 and 12.9 bolts needs baking to avoid hydrogen embrittlement. Zinc flake coatings avoid the risk.
Galvanic corrosion: which fastener in which metal?
In wet or salty conditions, two different metals form a battery and the less noble one corrodes. The fastener should be the more noble metal, because it is small next to the large part.
| Fastener ↓ / Part → | Carbon steel | Galvanised steel | Stainless steel | Aluminium | Copper / brass |
|---|---|---|---|---|---|
| Zinc-plated steel | ✓ | ✓ | ✕ | ! | ✕ |
| Stainless A2 / A4 | ✓ | ! | ✓ | ! | ✓ |
| Aluminium | ✕ | ! | ✕ | ✓ | ✕ |
| Brass / copper | ! | ✕ | ! | ✕ | ✓ |
| Titanium | ✓ | ! | ✓ | ! | ✓ |
✓ Good ! Use with care or isolate (nylon washer, sealant) ✕ Avoid in wet conditions
This page is a quick guide. For design and inspection, always check the current edition of the standard named on your drawing. Ask our team if you are unsure which grade, finish or size you need.