← AskMachinist · Guides · Calculator · 🔎 Search
Slotted Countersunk Screw Dimensions (ISO 2009 / DIN 963, M1.6 to M10)
Guide · Updated October 28, 2026
ISO 2009 covers slotted countersunk flat head screws, M1.6 to M10, product grade A; it replaced DIN 963. Values agree across the ISO 2009:2011 published table and the Lederer ISO 2009 catalog. Nominal values; check the standard for tolerances.
Need an exact reference size?
Build any gage block stack with the free Gage Block Calculator. Free, no login.
Step by step
- Find the thread: Pick the row for your thread size, M1.6 to M10.
- Cut the countersink: Use a 90° countersink and cut it to about dk plus a few tenths so the head sits flush.
- Pick the screwdriver: Match the blade to slot width n.
- Check the standard: ISO 2009 heads are bigger than DIN 963 from M3.5 up, so check which one your screws follow.
ISO 2009 slotted countersunk screw dimensions (mm)
Columns: thread d, pitch P, actual head diameter dk max, head height k max, slot width n nominal, slot depth t min.
- Size | P | dk | k | n | t
- M1.6 | 0.35 | 3 | 1 | 0.4 | 0.32
- M2 | 0.4 | 3.8 | 1.2 | 0.5 | 0.4
- M2.5 | 0.45 | 4.7 | 1.5 | 0.6 | 0.5
- M3 | 0.5 | 5.5 | 1.65 | 0.8 | 0.6
- (M3.5) | 0.6 | 7.3 | 2.35 | 1 | –
- M4 | 0.7 | 8.4 | 2.7 | 1.2 | –
- M5 | 0.8 | 9.3 | 2.7 | 1.2 | –
- M6 | 1 | 11.3 | 3.3 | 1.6 | 1.2
- M8 | 1.25 | 15.8 | 4.65 | 2 | –
- M10 | 1.5 | 18.3 | 5 | 2.5 | 2
Worked example: M4 flush in a panel
An M4 ISO 2009 head is 8.4 mm across and 2.7 mm high. Cut a 90° countersink to about 8.6 mm diameter so the head sits flush. A DIN 963 M4 head is only 7.5 mm, so the same countersink would leave it about 0.5 mm low.
Common problems
- Head sits proud or below the surface: the countersink was sized for the other standard; ISO 2009 and DIN 963 differ from M3.5 up.
- Head cracks or the panel splits: wrong countersink angle; use 90°, not 82° (inch).
- Slot strips: blade too small or not square to the slot; match blade to n and keep pressure on.
FAQ
Is DIN 963 the same as ISO 2009?
Not quite. Up to M3 they match. From M3.5 the ISO head is larger and lower; for example M4 is dk 8.4 / k 2.7 in ISO 2009 against 7.5 / 2.2 in DIN 963.
Why is dk called the actual head diameter?
ISO also gives a larger theoretical diameter at the sharp cone edge; the real head is slightly smaller because the edge is rounded or flat.
Why are some slot depths dashed?
For M3.5, M4, M5 and M8 the ISO table and the Lederer catalog give different minimum slot depths, so no value is shown.
What countersink angle?
90°, the same for ISO 2009, DIN 963 and ISO 10642 socket countersunk screws.
Related guides and calculators
- Slotted raised countersunk screws (ISO 2010)
- Phillips raised countersunk screws (ISO 7047)
- Phillips countersunk screws (ISO 7046)
- Phillips pan head screws (ISO 7045)
- Slotted pan head screws (ISO 1580)
- Slotted cheese head screws (ISO 1207)
- Countersunk socket screws (ISO 10642)
- Slotted set screws (ISO 4766)
- All free machinist calculators
Build your stack in seconds
The free Gage Block Calculator finds the fewest-block combination for inch and metric sets, with wear blocks. No login.
Questions? Ask a machinist.
General shop information only — follow your drawing, tool maker's data and your quality system.