This page covers M20 Button Head Socket Screws to ISO 7380: the full dimensional row, hole and tool sizes, proof-load data and typical applications. All values are taken from the governing standards (ISO 7380 together with ISO 273, ISO 724 and ISO 898-1 where applicable).
M20 Dimensional Row (ISO 7380)
| Size | Pitch (mm) | Head diameter dk (mm) | Head height k (mm) | Hex socket s (mm) | Reference standard |
|---|---|---|---|---|---|
| M20 | 2.5 | 35.0 | 11.0 | 12.0 | ISO 7380-1 / DIN 7380 |
Spanner & Drive for M20 Button Head Socket Screws
The hex socket for M20 Button Head Socket Screws is shown in the spec table — use the matching Allen / hex key (an ISO 2936 hex key set covers the full range). Ball-end keys are for reaching the screw, not for tightening it — finish on the plain end, and on production work use a torque-controlled driver.
Hole Sizes for M20
| Coarse-thread pitch (ISO 724) | 2.5 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 22 mm |
| Tapping drill, coarse thread | 17.5 mm |
Tightening Torque for M20
| Class 8.8 (dry, ~µ 0.125) | ≈ 420 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 598 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 700 Nm |
Indicative dry-joint values. Lubrication can lower the required torque by 15–25%. Always confirm against the joint design, especially when going up a strength class.
Proof Load & Strength for M20
This is a reduced-height head. The head, not the thread, limits what the screw will carry — ISO 7380-1 caps a button head at roughly 80% of the thread's capacity — so the thread's proof load overstates the assembly. Size the joint on the head, or use a cap screw where the full class strength is needed.
Installation Tips for M20 Button Head Socket Screws
- Use a quality Allen key fully seated in the socket — partial engagement is the most common cause of stripped sockets at this size.
- For countersunk and button-head variants, chamfer the through-hole to seat the head flush without preloading the head/shank fillet.
- At M20 the stretch in the bolt becomes the controlling factor — for critical joints, use angle-controlled or stretch-controlled tightening instead of pure torque.
Mating Parts for M20
For M20, pair with a M20 hex nut (ISO 4032 / DIN 934) and, where used, a M20 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.
Custom manufacturing · Made to drawing
Need button head socket screws in a size this table does not list?
This page covers M20 button head socket screws. Material and finish are usually what drives a special — a grade the standard part is not stocked in, or a coating chosen against a salt-spray figure instead of a default. Made by cold heading or warm forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
