Reference
Fastener Reference
Thread, hole and drive sizes for M3 to M8, and how to describe a part so the quote comes back right first time.
Threads & Holes
ISO metric threads. Tap drill for coarse thread; clearance holes per ISO 273.
| Size | Coarse pitch | Fine pitch | Tap drill | Clearance, fine | Medium | Coarse |
|---|---|---|---|---|---|---|
| M3 | 0.5 | 0.35 | 2.5 | 3.2 | 3.4 | 3.6 |
| M4 | 0.7 | 0.5 | 3.3 | 4.3 | 4.5 | 4.8 |
| M5 | 0.8 | 0.5 | 4.2 | 5.3 | 5.5 | 5.8 |
| M6 | 1.0 | 0.75 | 5.0 | 6.4 | 6.6 | 7.0 |
| M8 | 1.25 | 1.0 | 6.8 | 8.4 | 9.0 | 10.0 |
All values in mm. Coarse pitch is the default when a pitch isn't stated (M6 = M6 × 1.0).
Drive Sizes
Which tool fits which screw.
| Size | Hex head spanner (ISO 4017) | Socket cap key (ISO 4762) | Button head key (ISO 7380) | Phillips pan (ISO 7045) | Torx pan (ISO 14583) |
|---|---|---|---|---|---|
| M3 | 5.5 | 2.5 | 2 | PH1 | T10 |
| M4 | 7 | 3 | 2.5 | PH2 | T20 |
| M5 | 8 | 4 | 3 | PH2 | T25 |
| M6 | 10 | 5 | 4 | PH3 | T30 |
| M8 | 13 | 6 | 5 | PH4 | T45 |
Spanner and key sizes in mm. Older DIN sizes differ from ISO at some diameters, so check against your drawing.
Choosing a Material
| Material | Corrosion resistance | Magnetic | Needs plating | Typical use |
|---|---|---|---|---|
| Mild steel | Low unless plated | Yes | Yes | Most screws and bolts; indoor or plated |
| Stainless A2 (304) | Good | Slightly, after forming | No | General outdoor, food and electrical |
| Stainless A4 (316) | Very good | Slightly, after forming | No | Coastal, chemical, solar sites |
| Brass | Good | No | No | Turned parts, nozzles, inserts, electrical |
Finishes and what each one is for: materials & finishes →
Describing a Part
A full description in one line saves a round of questions. For a custom part, a drawing or a sample photo with dimensions replaces most of this.
| Give | Example |
|---|---|
| Product & standard | Pan Phillips screw, ISO 7045 |
| Thread × length | M4 × 12 (length under the head; overall for countersunk) |
| Material / class | Stainless A2-70, or steel property class 4.8 |
| Finish | Plain, or e.g. trivalent zinc |
| Quantity | 10,000 pcs per order |