No.4 (3mm) Slotted Countersunk Wood Screws DIN 97 A2 Stainless
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- Standard DIN 97
- Stainless grade A2 (304)
- Drive Slotted
- Head angle 90°
How to measure DIN 97 slotted countersunk wood screws
Gauge to thread size
- No.32.5mm
- No.43mm
- No.63.5mm
- No.84mm
- No.105mm
- No.125.5mm
| Dimension | Symbol | Value |
|---|---|---|
| Thread diameter (nominal) | d | 3.0 mm |
| Shank diameter | ds | 2.6 to 3.0 mm |
| Head diameter | dk | 5.6 mm |
| Head height (max) | k | 1.65 mm |
| Slot width | n | 0.8 mm |
| Slot depth | t | 0.6 to 0.85 mm |
| Lengths available (overall, including head) | L | 10, 12, 16, 20, 25, 30, 35, 40 mm |
No.4 (3mm) slotted countersunk wood screws to DIN 97, in A2 stainless steel. The head pulls flush with the surface in a countersunk hole, and the single slot takes a flat-blade screwdriver.
A2 stainless holds up well outdoors, so these suit cladding, garden work and general joinery as well as indoor fixings. Buy one or a thousand, there's no minimum order.
What these are used for
Slotted countersunk screws are the classic wood screw. They're the right look for repairs to old doors, furniture and joinery, where a cross-head would look out of place. The head finishes flush, so nothing catches on a hinge leaf or a lid.
If you'd rather have a cross-head, our No.4 pozi countersunk wood screws have the same head with a PZ1 recess.
They're partly threaded, with a plain shank under the head. Drill a clearance hole in the top piece and the screw draws the two pieces of timber tight together.
The underside of the head is a 90° cone, so a standard 90° countersink bit gives a flush fit. Imperial flat head screws made to the US standard have an 82° head, so they don't match a 90° countersink exactly.
Choosing the right size
The gauge number sets the thickness, and the higher the number, the thicker the screw. A No.4 is 3mm across the thread, between the No.3 (2.5mm) and the No.6 (3.5mm).
Length on a countersunk screw is measured overall, from the top of the head to the point, because the whole screw ends up in the wood. The No.4 comes in 8 lengths from 10mm to 40mm.
The 3mm is the nominal thread size, and across the thread a new No.4 measures 3mm or a touch under. The plain shank under the head can be thinner, down to 2.6mm. That's normal, and both figures are in the dimensions table.
Material and grade
A2 is the everyday stainless grade for fixings, the same family as 304 and 18/8. It copes with rain and damp, which is why it's the usual choice for outdoor timber. It's close to non-magnetic, though a slight pull on a magnet is normal.
Salt is a different matter. Near the sea or a pool, A4 lasts longer. Our guides to A2 stainless steel and A4 stainless steel explain the difference.
Common questions
What size is a No.4 screw in mm?
A No.4 wood screw is 3mm across the thread. These are made to DIN 97, which also sets the head: 5.6mm across, 1.65mm high at most, with a 0.8mm slot.
The No.4 name is a trade size. Ours are metric screws with a 3mm thread, the nearest metric match to an imperial No.4, which measures about 2.8mm.
What's the difference between these and raised head screws?
These DIN 97 screws have a flat top that finishes flush with the surface. Raised head screws (DIN 95) have the same countersunk underside with a shallow dome on top, so the head sits slightly proud. If that's the look you want, see our No.4 slotted raised head wood screws.
What is a No.4 x 1 inch screw in mm?
The nearest metric size is 3 x 25mm. Wood screws are still often asked for in inches, so each length here shows both, such as 1/2in (12mm), 1in (25mm) and 1 1/2in (40mm). The screws are made to the metric length, and the inch size is the closest imperial equivalent, so a 1in screw here is 25mm rather than 25.4mm.
How do I measure a No.4 screw?
Measure across the outside of the thread with a caliper. A new No.4 will read 3mm or a touch under, because 3mm is the nominal thread size. The plain shank under the head is a separate measurement and can be thinner, as DIN 97 allows it to be as small as 2.6mm.
For length, measure overall, from the flat top of the head to the tip.