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Thin Castle Nut Dimensions (DIN 937, M6 to M24)

Guide · Updated October 28, 2026

DIN 937 covers thin (low form) hex slotted and castle nuts. Pitch P, wrench size s, height m, crown diameter de, slot width n, w max and the DIN 94 split pin agree across the fasteners.eu DIN 937 table, the Ferrobend DIN 937 table and the Aspen Fasteners DIN 937 sheet. M12 e min is left out: fasteners.eu and Ferrobend list 20.1 mm and Aspen lists 21.1 mm. Not shown: M7, M22 (e min conflicts: 35.03 vs 37.29 mm), fine-pitch rows and M27 and up. Check the current edition or your supplier for critical work.

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Step by step

Confirm the size: DIN 937 is the thin (low) slotted and castle nut. Up to M10 the slots are cut into the hex; from M12 up they are in a turned round crown. This chart shows M6 to M24 coarse pitch.
Pick the wrench: s is the wrench size: M8 13 mm, M10 17 mm, M12 19 mm, M16 24 mm, M20 30 mm. DIN 937 keeps the older 17 / 19 / 22 mm sizes for M10 / M12 / M14.
Check the height: m is the total nut height including the slots: M10 9 mm, M12 10 mm, M16 12 mm, M24 15 mm.
Check the slot: n is the slot width: M12 3.5 to 3.8 mm. w max is the height from the bearing face to the slot bottom: M12 6 mm.
Pick the split pin: Use the DIN 94 split pin listed: M8 2 x 16, M12 3.2 x 22, M16 4 x 28, M20 4 x 36.
Drill the bolt: Drill the cross hole so it lines up inside the slot (below the slot top, above w). Tighten to torque and go forward to the next slot, never back off.

DIN 937 thin castle nut dimensions (mm)

Columns: thread size, coarse pitch P, wrench size s, width across corners e min, nut height m max, crown diameter de max (M12 and up), slot width n min–max, slot bottom height w max, DIN 94 split pin. Sizes in brackets are non-preferred.

Size | P | s | e min | m | de | n | w max | split pin
M6 | 1 | 10 | 11.05 | 6 | — | 2–2.25 | 3.5 | 1.6 x 14
M8 | 1.25 | 13 | 14.38 | 8 | — | 2.5–2.75 | 4.5 | 2 x 16
M10 | 1.5 | 17 | 18.9 | 9 | — | 2.8–3.05 | 5 | 2.5 x 20
M12 | 1.75 | 19 | see note | 10 | 17 | 3.5–3.8 | 6 | 3.2 x 22
(M14) | 2 | 22 | 24.49 | 11 | 19 | 3.5–3.8 | 7 | 3.2 x 25
M16 | 2 | 24 | 26.75 | 12 | 22 | 4.5–4.8 | 7 | 4 x 28
(M18) | 2.5 | 27 | 29.56 | 13 | 25 | 4.5–4.8 | 8 | 4 x 32
M20 | 2.5 | 30 | 32.95 | 13 | 28 | 4.5–4.8 | 8 | 4 x 36
M24 | 3 | 36 | 39.55 | 15 | 34 | 5.5–5.8 | 9 | 5 x 40

Worked example: M16 thin castle nut

An M16 DIN 937 nut takes a 24 mm wrench, stands 12 mm tall, has a 22 mm max crown and its slot bottoms are at most 7 mm above the bearing face. Put the bolt cross hole about 7 to 11 mm above the washer face so the 4 x 28 split pin passes through a slot. The same size in DIN 935 is 19 mm tall, so the thin nut saves 7 mm of stick-out.

DIN 937 vs DIN 935 at a glance

M10: DIN 937 17 mm wrench, 9 mm tall; DIN 935 16 mm wrench, 12 mm tall.
M12: DIN 937 19 mm, 10 mm tall; DIN 935 18 mm, 15 mm tall.
M16: both 24 mm wrench; DIN 937 12 mm tall, DIN 935 19 mm tall.
Split pins are the same DIN 94 sizes for M6 to M16.

Common problems

Backing off to align a slot: this drops clamp load. Go forward to the next slot within the torque range.
Hole drilled too high or low: the pin misses the slot or the nut cannot reach torque.
Reusing split pins: fit a new pin every time.
Mixing up nut families: DIN 937 M10 / M12 use 17 / 19 mm wrenches, not the 16 / 18 mm of current DIN 935.
Thin nut on a high-load joint: use the regular DIN 935 height instead.

FAQ

What is a DIN 937 nut?

A thin (low form) hex slotted or castle nut. It takes a split pin through radial slots like DIN 935, but is lower, for tight spaces or light loads.

How is DIN 937 different from DIN 935?

DIN 937 is lower: M12 is 10 mm tall versus 15 mm for DIN 935, and M16 is 12 mm versus 19 mm. DIN 937 also keeps the 17 / 19 / 22 mm wrench sizes for M10 / M12 / M14, while current DIN 935 uses 16 / 18 / 21 mm.

What wrench fits a DIN 937 M12 castle nut?

19 mm. M10 is 17 mm and M16 is 24 mm.

What split pin fits a DIN 937 nut?

DIN 94 pins: M6 1.6 x 14, M8 2 x 16, M10 2.5 x 20, M12 3.2 x 22, M16 4 x 28, M20 4 x 36, M24 5 x 40.

Can a thin castle nut take full bolt load?

Not as a rule. Low nuts strip at lower load than regular height nuts. Use DIN 935 where full preload is needed, and check the property class with your supplier.

Are M14 and M18 standard?

They are non-preferred sizes (in brackets) and harder to buy.

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