M3 is one of the standard coarse-thread sizes for slotted countersunk head screw under GB/T 68 / ISO 2009. The sections below reproduce the dimensional row, list the matching tools and hole sizes, and summarize where this size is normally specified.
M3 Dimensional Row (GB/T 68 / ISO 2009)
| Size | Pitch (mm) | Length L (mm) | Head diameter dk (mm) | Head height k (mm) | Cross recess | Countersink angle (deg) | Reference standard |
|---|---|---|---|---|---|---|---|
| M3 | 0.5 | 20 | 5.6 | 1.65 | PH1 | 90 | ISO 7046 / GB/T 819 |
Spanner & Drive for M3 Slotted Countersunk Head Screw — GB/T 68 / ISO 2009 (Series 039)
The hex socket for M3 Slotted Countersunk Head Screw — GB/T 68 / ISO 2009 (Series 039) is shown in the spec table — use the matching Allen / hex key (an ISO 2936 hex key set covers the full range). For a one-off, a T-handle key and a calibrated arm will do. For a batch, the only way to get the same preload twice is a torque-controlled driver.
Hole Sizes for M3
| Coarse-thread pitch (ISO 724) | 0.5 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 3.4 mm |
| Tapping drill, coarse thread | 2.5 mm |
Tightening Torque for M3
| Class 8.8 (dry, ~µ 0.125) | ≈ 1.3 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 2.2 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 M3
| Tensile stress area As (ISO 724) | 5 mm² |
|---|---|
| Proof load, class 8.8 | 2.9 kN |
| Proof load, class 12.9 | 4.9 kN |
| Min. ultimate tensile load, class 8.8 | 4 kN |
Proof load = tensile stress area × the proof stress Sp of the class, per ISO 898-1 — Sp is a lower figure than the yield stress Rp0.2 and the two are not interchangeable. The stress area is computed from this size's own diameter and pitch, so a fine-pitch designation gives the fine-pitch figure. Design the joint so the working preload stays below the proof load of the class selected.
M3 Slotted Countersunk Head Screw — GB/T 68 / ISO 2009 (Series 039) Weight
A steel M3 slotted countersunk head screw at the listed 20 mm length weighs approximately 3.9 g each — about 3.9 kg per 1,000 pieces. Stainless A2/A4 weighs roughly the same (density 7.9–8.0 g/cm³).
Actual weight varies slightly with head form, thread and finish; use this figure for freight estimation only.
Installation Tips for M3 Slotted Countersunk Head Screw — GB/T 68 / ISO 2009 (Series 039)
- 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 M3 the joint is sensitive to over-torque — use a torque-limiting driver and check the head doesn't bury into a softer counterpart.
Mating Parts for M3
For M3, pair with a M3 hex nut (ISO 4032 / DIN 934) and, where used, a M3 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.
Custom manufacturing · Made to drawing
Need slotted countersunk head screw in a size this table does not list?
This page covers M3 slotted countersunk head screw. 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.
