Fastening
Hex socket screws
The four families that show up in mold bases: socket head cap, countersunk, set screws and shoulder screws. With the ISO 273 clearance hole, the counterbore, the right length by each standard's convention, and torque from the thread stress area.
The standard mold-base screw. The head sits in a counterbore, and it carries the highest clamp load of the four families.
1. Size
- Pitch
- 1.25
- Head dk
- 13.00
- Height k
- 8.00
- Key s
- 6.00
2. Plate and counterbore
The counterbore comes from the head Ø plus the clearance. DIN 974-1 tabulates preferred values; here you match your own shop standard.3. Thread and tightening
K ≈ 0.20 dry and 0.14 lubricated. It's the biggest source of uncertainty in torque tightening: the scatter in K alone is worth ±25% of the preload.Clearance hole
9.00
mm
Counterbore Ø
14.00
× 8.50 mm
Length
25
mm · min. 24.5
Torque
45.1
N·m · class 12.9
Drilling and tightening
| Clearance hole | 9.00 mm | Medium (H13) |
|---|---|---|
| Counterbore Ø | 14.00 mm | head 13.00 + clearance |
| Depth | 8.50 mm | |
| Material under the counterbore | 16.50 mm | |
| Minimum thread engagement | 8.00 mm | 1× d |
| Minimum length | 24.5 mm | length under the head |
| Preferred length | 25 mm | ISO 888 |
| Thread stress area | 36.6 mm² | ISO 898-1 |
| Target preload | 28.2 kN | 70% of Rp0.2 |
| Tightening torque | 45.1 N·m | T = K·d·F, K = 0.2 |
Four details that wreck a design
Length isn't measured the same way in both
In DIN 912 the nominal length is measured under the head. In DIN 7991 it is the overall length, head included — because the head sits inside the plate.
Mixing the two conventions is the classic mistake: the screw arrives and there isn't enough thread. The tool calculates with the chosen family's convention, and says which one it's using.
The countersunk head self-centres
The 90° cone touches the countersink wall all the way round and pulls the screw to the centre of the hole. That cancels the clearance in the through hole: the part goes where the countersink says, not where you set it.
Where the assembly needs adjustment, use a cap head with a clearance hole — and let a dowel or a shoulder screw do the locating.
A set screw's key is smaller
Same thread, different key: an M6 cap screw takes a 5 mm key; an M6 set screw takes a 3 mm one. The set screw's socket has to fit inside the thread diameter.
The practical consequence: a set screw takes far less tightening torque before the socket strips.
A shoulder screw only pays off in an H7 hole
What a shoulder screw sells is the ground shoulder working in a reamed H7 hole — it locates and clamps in the same element, replacing a dowel plus a screw.
In a merely drilled hole, it's an expensive ordinary screw. And the shoulder must be longer than the plate it passes through: if it isn't, the head clamps against the shoulder instead of the plate, and the joint stays loose.
About the counterbore
DIN 974-1 tabulates preferred counterbore diameters, but it's a paid standard, and the only accessible secondary source disagrees with it — giving a depth equal to the head height, while the standard allows clearance. With a single source and a conflict, tabulating it here would be inventing.
So the counterbore is calculated: from the head Ø and height — both confirmed in three independent lookups — plus the clearance you choose. It stays traceable and adjustable to your shop standard. Anyone who needs a hole to the standard should check DIN 974-1.
DIN 912 / ISO 4762 — socket head cap screw
| Thread | Pitch | Head dk | Height k | Key s | Socket depth t |
|---|---|---|---|---|---|
| M1.6 | 0.35 | 3.00 | 1.60 | 1.50 | 0.70 |
| M2 | 0.40 | 3.80 | 2.00 | 1.50 | 1.00 |
| M2.5 | 0.45 | 4.50 | 2.50 | 2.00 | 1.10 |
| M3 | 0.50 | 5.50 | 3.00 | 2.50 | 1.30 |
| M4 | 0.70 | 7.00 | 4.00 | 3.00 | 2.00 |
| M5 | 0.80 | 8.50 | 5.00 | 4.00 | 2.50 |
| M6 | 1.00 | 10.00 | 6.00 | 5.00 | 3.00 |
| M8 | 1.25 | 13.00 | 8.00 | 6.00 | 4.00 |
| M10 | 1.50 | 16.00 | 10.00 | 8.00 | 5.00 |
| M12 | 1.75 | 18.00 | 12.00 | 10.00 | 6.00 |
| M14 | 2.00 | 21.00 | 14.00 | 12.00 | 7.00 |
| M16 | 2.00 | 24.00 | 16.00 | 14.00 | 8.00 |
| M20 | 2.50 | 30.00 | 20.00 | 17.00 | 10.00 |
| M24 | 3.00 | 36.00 | 24.00 | 19.00 | 12.00 |
| M30 | 3.50 | 45.00 | 30.00 | 22.00 | 15.50 |
| M36 | 4.00 | 54.00 | 36.00 | 27.00 | 19.00 |
DIN 7991 / ISO 10642 — 90° countersunk head
| Thread | Pitch | Head dk | Height k | Key s | Socket depth t |
|---|---|---|---|---|---|
| M3 | 0.50 | 6.00 | 1.70 | 2.00 | — |
| M4 | 0.70 | 8.00 | 2.30 | 2.50 | — |
| M5 | 0.80 | 10.00 | 2.80 | 3.00 | — |
| M6 | 1.00 | 12.00 | 3.30 | 4.00 | — |
| M8 | 1.25 | 16.00 | 4.40 | 5.00 | — |
| M10 | 1.50 | 20.00 | 5.50 | 6.00 | — |
| M12 | 1.75 | 24.00 | 6.50 | 8.00 | — |
| M14 | 2.00 | 27.00 | 7.00 | 10.00 | — |
| M16 | 2.00 | 30.00 | 7.50 | 10.00 | — |
| M18 | 2.50 | 33.00 | 8.00 | 12.00 | — |
| M20 | 2.50 | 36.00 | 8.50 | 12.00 | — |
DIN 913 to 916 — set screws
The four standards differ only in the point; thread and socket are the same. Choosing the point is in the tool above.
| Thread | Pitch | Key s | Socket depth t |
|---|---|---|---|
| M3 | 0.50 | 1.50 | — |
| M4 | 0.70 | 2.00 | — |
| M5 | 0.80 | 2.50 | — |
| M6 | 1.00 | 3.00 | — |
| M8 | 1.25 | 4.00 | — |
| M10 | 1.50 | 5.00 | — |
| M12 | 1.75 | 6.00 | — |
| M16 | 2.00 | 8.00 | — |
| M20 | 2.50 | 10.00 | — |
ISO 7379 — shoulder screw
| Shoulder ds | Thread | Pitch | dk max. | k max. | Key | Min. thread b |
|---|---|---|---|---|---|---|
| Ø6 | M5 | 0.80 | 10.22 | 4.50 | 3.00 | 9.50 |
| Ø8 | M6 | 1.00 | 13.27 | 5.50 | 4.00 | 11.00 |
| Ø10 | M8 | 1.25 | 16.27 | 7.00 | 5.00 | 13.00 |
| Ø12 | M10 | 1.50 | 18.27 | 8.90 | 6.00 | 16.00 |
| Ø16 | M12 | 1.75 | 24.33 | 10.11 | 8.00 | 18.00 |
| Ø20 | M16 | 2.00 | 30.33 | 14.00 | 10.00 | 22.00 |
| Ø24 | M20 | 2.50 | 36.39 | 16.00 | 12.00 | 27.00 |
A single source, unlike the other tables on this page — check before machining the H7 hole.
ISO 273 — clearance hole
Checked row by row between two independent sources. The medium series is general use; the close one, for joints located by dowels; the free one, where the hole's positional tolerance is wide.
| Thread | Close H12 | Medium H13 | Free H14 |
|---|---|---|---|
| M1.6 | 1.70 | 1.80 | 2.00 |
| M2 | 2.20 | 2.40 | 2.60 |
| M2.5 | 2.70 | 2.90 | 3.10 |
| M3 | 3.20 | 3.40 | 3.60 |
| M4 | 4.30 | 4.50 | 4.80 |
| M5 | 5.30 | 5.50 | 5.80 |
| M6 | 6.40 | 6.60 | 7.00 |
| M8 | 8.40 | 9.00 | 10.00 |
| M10 | 10.50 | 11.00 | 12.00 |
| M12 | 13.00 | 13.50 | 14.50 |
| M14 | 15.00 | 15.50 | 16.50 |
| M16 | 17.00 | 17.50 | 18.50 |
| M18 | 19.00 | 20.00 | 21.00 |
| M20 | 21.00 | 22.00 | 24.00 |
| M22 | 23.00 | 24.00 | 26.00 |
| M24 | 25.00 | 26.00 | 28.00 |
| M30 | 31.00 | 33.00 | 35.00 |
| M36 | 37.00 | 39.00 | 42.00 |