Hex key (Allen wrench) size, key depth and point sizes for metric socket set screws, M1.6 to M24 — flat (DIN 913), cone (DIN 914), dog (DIN 915) and cup point (DIN 916).
A metric set screw is sized by its thread — M6 is 6 mm across the thread — and measured overall, end to end, in millimetres. It has no head: the hex key (Allen wrench) goes into a socket in one end, and the other end is the point that bears on the shaft. All four DINs take the same hex key at the same size; they differ only in the point. DIN 913–916 match ISO 4026–4029.
| Size | Pitch | Hex key s | Key depth t min, short screws | Key depth t min, longer screws |
|---|---|---|---|---|
| M1.6 | 0.35 | 0.7 mm | 0.7 | 1.5 |
| M2 | 0.4 | 0.9 mm | 0.8 | 1.7 |
| M2.5 | 0.45 | 1.3 mm | 1.2 | 2 |
| M3 | 0.5 | 1.5 mm | 1.2 | 2 |
| M4 | 0.7 | 2 mm | 1.5 | 2.5 |
| M5 | 0.8 | 2.5 mm | 2 | 3 |
| M6 | 1 | 3 mm | 2 | 3.5 |
| M8 | 1.25 | 4 mm | 3 | 5 |
| M10 | 1.5 | 5 mm | 4 | 6 |
| M12 | 1.75 | 6 mm | 4.8 | 8 |
| M16 | 2 | 8 mm | 6.4 | 10 |
| M20 | 2.5 | 10 mm | 8 | 12 |
| M24 | 3 | 12 mm | 10 | 15 |
| Size | Flat dia max (913) | Cone tip max (914) | Dog dia max (915) | Dog z (short / long) | Short dog to L | Cup dia max (916) |
|---|---|---|---|---|---|---|
| M1.6 | 0.8 | — | 0.8 | 0.4–0.65 / 0.8 min | 2.5 | 0.8 |
| M2 | 1 | — | 1 | 0.5 min / 1–1.25 | 3 | 1 |
| M2.5 | 1.5 | — | 1.5 | 0.63–0.88 / 1.25–1.5 | 4 | 1.2 |
| M3 | 2 | sharp | 2 | 0.75–1 / 1.5–1.75 | 5 | 1.4 |
| M4 | 2.5 | sharp | 2.5 | 1–1.25 / 2–2.25 | 6 | 2 |
| M5 | 3.5 | sharp | 3.5 | 1.25–1.5 / 2.5–2.75 | 6 | 2.5 |
| M6 | 4 | 1.5 | 4 | 1.5–1.75 / 3–3.25 | 8 | 3 |
| M8 | 5.5 | 2 | 5.5 | 2–2.25 / 4–4.3 | 10 | 5 |
| M10 | 7 | 2.5 | 7 | 2.5–2.75 / 5–5.3 | 12 | 6 |
| M12 | 8.5 | 3 | 8.5 | 3–3.25 / 6–6.3 | 16 | 8 |
| M16 | 12 | — | 12 | 4–4.3 / 8–8.36 | 20 | 10 |
| M20 | 15 | — | 15 | 5–5.3 / 10–10.36 | 25 | 14 |
| M24 | 18 | — | 18 | 6–6.3 / 12–12.43 | 30 | 16 |
Good to know
Cup point is the everyday choice — its edge bites into the shaft. Flat point for parts you adjust often or a shaft with a flat; dog point to sit in a hole or slot in the shaft; cone point to locate in a drilled spot. Inch set screws are on the set screw chart; metric thread pitches on the metric thread pitch chart.
Quick answers
- What size Allen key fits an M6 set screw?
- A 3 mm hex key — the same for flat, cone, dog and cup point (DIN 913 / 914 / 915 / 916).
- What hex key goes with each metric set screw?
- M1.6 – 0.7 mm, M2 – 0.9 mm, M2.5 – 1.3 mm, M3 – 1.5 mm, M4 – 2 mm, M5 – 2.5 mm, M6 – 3 mm, M8 – 4 mm, M10 – 5 mm, M12 – 6 mm, M16 – 8 mm, M20 – 10 mm, M24 – 12 mm.
- How big is the cup on an M8 cup point set screw?
- 5 mm across, maximum (DIN 916).
- How deep does the hex key go in an M10 set screw?
- At least 4 mm in a short screw, 6 mm in a longer one.
- How is a metric set screw measured?
- Overall, end to end, in millimetres; the size is the thread (M6 = 6 mm).