Thread Standard Cross-Reference: ISO vs DIN vs ASME vs GB
A drawing calls for an M8 × 25 8.8 bolt. The customer's maintenance manual lists a 5/16-18 × 1 DIN 933. The supplier ships a 1/4-20. Three threads, three standards, and a field failure waiting to happen. Cross-referencing bolt standards is not as simple as looking up a size chart — the thread pitch, head size, wrench clearance and property class all shift when you jump between ISO, DIN, ASME and GB.
The short answer: metric M ≈ imperial only on diameter and length, never on pitch or head size. When a drawing switches standards, re-verify the wrench clearance and the proof load, do not assume a drop-in replacement.
Common bolt standard cross-reference
| Description | ISO | DIN | ASME / ASTM | GB (China) |
|---|---|---|---|---|
| Hex bolt, full thread | ISO 4017 | DIN 933 | ASME B18.2.1 / ASTM F593 | GB/T 5783 |
| Hex bolt, partial thread | ISO 4014 | DIN 931 | ASME B18.2.1 | GB/T 5782 |
| Hex nut | ISO 4032 | DIN 934 | ASME B18.2.2 | GB/T 6170 |
| Socket head cap screw | ISO 4762 | DIN 912 | ASME B18.3 / ASTM F835 | GB/T 70.1 |
| Property class / grade | ISO 898-1 (8.8/10.9/12.9) | DIN EN ISO 898-1 | ASTM A325 / A490 / F3125 | GB/T 3098.1 |
| Stainless grade | ISO 3506 (A2-70/A4-80) | DIN EN ISO 3506 | ASTM F593 (304/316) | GB/T 3098.6 |
The three things that do not translate across standards
1. Thread pitch is not interchangeable. An M8 × 1.25 coarse thread does not mate with a 5/16-18 (which is actually closer to M8 × 1.0). The minor diameter, tap drill and engagement length are all different. Never tap an imperial hole with a metric bolt or vice versa.
2. Head size and wrench clearance differ. An M8 hex bolt under DIN 933 uses a 13 mm wrench. A 5/16-18 hex bolt under ASME B18.2.1 uses a 1/2 inch (12.7 mm) wrench. Close, but not the same — and a 1 mm difference strips flats on repeated use. Always re-verify the socket or wrench when cross-substituting.
3. Property class ≠ grade number. AISI/ASTM A325 is roughly equivalent to metric 8.8, and A490 roughly to 10.9 — but the proof load, hardness range and dimensional tolerances are not identical. For safety-critical joints, use the exact standard on the drawing, not a "near equivalent."
Practical rule for procurement
When a customer switches from a DIN 933 M8 × 25 8.8 to an ASME B18.2.1 5/16-18 × 1 Grade 5, the replacement works in the assembly only if (a) the hole clearance allows the slightly larger imperial head, (b) the torque chart is re-derived for the different friction, and (c) the coating and plating meet the same salt-spray spec. Anything less is a field return waiting to happen.
Toprecision manufactures to ISO, DIN, ASME and GB standards, and can cross-reference drawings from any of the four systems. Send the original drawing and the target standard — we will flag the dimensions that do not translate and recommend the exact equivalent. Request a standard cross-reference with full dimensional and property-class verification.
