How to Read a Screw Spec
One complete spec line gets you an accurate quote — e.g. Hex bolt M8×1.25×30 · class 8.8 · zinc plated · GB/T 5783. It is only five segments once you break it down.
| Segment | Example | Meaning |
|---|---|---|
| (1) Type | Hex bolt | Head style & use: hex bolt, socket cap screw, countersunk, flange… |
| (2) Thread & length | M8×1.25×30 | 8 mm nominal dia.; 1.25 pitch (omit for coarse); 30 mm length |
| (3) Grade / material | Class 8.8 | Carbon steel 4.8 / 8.8 / 10.9 / 12.9, or stainless A2-70 (304) / A4-80 (316) |
| (4) Surface finish | Zinc plated | Clear zinc, blue-white, yellow, hot-dip galvanising, Dacromet, black oxide… |
| (5) Standard | GB/T 5783 | GB / DIN / ISO / ANSI code — sets head detail and tolerance |
Common Spec Mistakes
- Writing only "M8 screw" — no length, grade or head type, so nobody can quote.
- Mixing screw / bolt — a bolt mates with a nut; a screw drives into the workpiece.
- Omitting the standard — same spec differs between GB/T 5783 and DIN 933; always state it.
Fill in these five segments and you will get an accurate quotation in one round. For a full RFQ checklist see How to get a fastener quote quickly.