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Slotted Set Screw Dimensions (ISO 4766 / DIN 551, M1.6 to M12)
Guide · Updated October 28, 2026
ISO 4766 covers slotted set screws with flat point (DIN 551), from M1.6 to M12. Values agree across fasten.it (DIN 551 and ISO 4766), fasteners.eu, Torqbolt and DigiPich, and conflicting cells are dashed. Check your supplier for critical work.
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Step by step
- Read the thread: Measure the major diameter and pitch. The chart covers coarse M1.6 to M12.
- Pick the screwdriver: Choose a blade that fills the slot width n, at least n nom thick, and is as wide as the screw.
- Check the point: dp is the flat point diameter. Leave a flat on the shaft wider than dp max.
- Mind the torque: A slot carries much less torque than a hex socket. Use ISO 4026 socket set screws where you need a higher clamp.
- Lock it: Add threadlocker for vibration.
ISO 4766 slotted set screw dimensions (mm)
Columns: thread, pitch P, slot width n nom, min and max, slot depth t min and max, flat point diameter dp max and min.
- Size | P | n nom | n min | n max | t min | t max | dp max | dp min
- M1.6 | 0.35 | 0.25 | 0.31 | 0.45 | 0.56 | 0.74 | 0.8 | 0.55
- M2 | 0.4 | 0.25 | 0.31 | 0.45 | 0.64 | 0.84 | 1 | 0.75
- M2.5 | 0.45 | 0.4 | 0.46 | 0.6 | 0.72 | 0.95 | 1.5 | 1.25
- M3 | 0.5 | 0.4 | 0.46 | 0.6 | 0.8 | 1.05 | 2 | 1.75
- (M3.5) | 0.6 | 0.5 | 0.56 | 0.7 | 0.96 | 1.21 | 2.2 | 1.95
- M4 | 0.7 | 0.6 | 0.66 | 0.8 | 1.12 | — | 2.5 | 2.25
- M5 | 0.8 | 0.8 | 0.86 | 1 | 1.28 | 1.63 | 3.5 | 3.2
- M6 | 1 | 1 | 1.06 | 1.2 | 1.6 | 2 | 4 | 3.7
- M8 | 1.25 | 1.2 | 1.26 | 1.51 | 2 | 2.5 | 5.5 | 5.2
- M10 | 1.5 | 1.6 | 1.66 | 1.91 | 2.4 | 3 | 7 | —
- M12 | 1.75 | 2 | 2.06 | 2.31 | 2.8 | 3.6 | 8.5 | 8.14
Worked example: M5 slotted grub screw
An M5 slotted set screw has a slot 0.86 to 1.0 mm wide and 1.28 to 1.63 mm deep, so use a 0.8 mm screwdriver blade. Its flat point is 3.2 to 3.5 mm across.
Common problems
- Slot cams out: use a blade that fills the slot, or switch to a socket set screw.
- Slot is damaged: drill it out, or grip it with an extractor.
- Screw loosens: add threadlocker.
FAQ
What is ISO 4766?
The slotted set screw with flat point, a headless grub screw turned with a flat screwdriver. DIN 551 is the German equivalent with the same dimensions.
Slotted or socket set screw?
Slotted screws are cheap and fine for light clamping, knobs and adjusters. Hex socket set screws (ISO 4026 to 4029) take far more torque.
Why are some cells dashed?
Sources disagree on t max at M4 (1.42 vs 1.45) and dp min at M10 (6.64 vs 6.67), so those cells are dashed.
What about DIN 553?
DIN 553 (ISO 7434) is the cone point version. It shares the slot sizes, but its point values were not confirmed this wave.
What was skipped?
The DIN-only sizes M1 to M1.4, the cone point (DIN 553), and the two dashed cells.
Related guides and calculators
- Slotted countersunk screws (ISO 2009)
- Slotted cheese head screws (ISO 1207)
- Slotted cup point set screws (ISO 7436)
- Slotted dog point set screws (ISO 7435)
- Slotted cone point set screws (ISO 7434)
- Flat point set screws (ISO 4026)
- Cup point set screws (ISO 4029 / DIN 916)
- Cone point set screws (ISO 4027 / DIN 914)
- Dog point set screws (ISO 4028 / DIN 915)
- All free machinist calculators
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