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Clamping Washer Dimensions (DIN 6340, M6 to M30)

Guide · Updated October 28, 2026

DIN 6340 covers washers for clamping devices. The bore d1, outside diameter d2 and thickness s below agree across the Elesa+Ganter DIN 6340 sheet, the Dold Mechatronik DIN 6340 sheet and the Daniel Gruppe DIN 6340 technical data sheet. Skipped: size 15 (M14), which two catalogs sell but also note is not on the official standard sheet. Check the current edition (DIN 6340:1987-04) or your supplier for critical work.

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Step by step

Match the stud: Pick the washer by the stud thread: M12 stud takes DIN 6340-13, M16 takes DIN 6340-17, M20 takes DIN 6340-21.
Check the bore: Bore d1 is a medium clearance hole (6.4 for M6, 13 for M12), so the washer slides freely over the stud.
Check the outside diameter: The large d2 (about 2.7 to 2.9 times the thread) spans slotted holes in strap clamps without dishing in.
Allow for thickness: Add s (3 mm on M6 up to 10 mm on M30) to your stud length stack-up.
Place it under the nut: Put the hardened washer between the strap clamp and the DIN 6331 collar nut or hex nut.
Torque the nut: Tighten the nut; the hardened face spreads load and stops the nut biting into the clamp.

DIN 6340 clamping washer dimensions (mm)

Columns: stud thread, bore d1, outside diameter d2, thickness s. Catalog designation is DIN 6340 plus d1, e.g. DIN 6340-13.

Thread | Bore d1 | Outside d2 | Thickness s
M6 | 6.4 | 17 | 3
M8 | 8.4 | 23 | 4
M10 | 10.5 | 28 | 4
M12 | 13 | 35 | 5
M16 | 17 | 45 | 6
M20 | 21 | 50 | 6
M24 | 25 | 60 | 8
M30 | 31 | 68 | 10

Worked example: M16 clamping stack

On an 18 mm slot with a DIN 508 M16 nut and DIN 6379 stud, a 25 mm strap, the 6 mm DIN 6340-17 washer and a 24 mm DIN 6331 collar nut need 25 + 6 + 24 = 55 mm, plus about 5 mm spare: 60 mm of top thread. The 100-63 stud fits.

DIN 6340 vs DIN 125 vs DIN 6796

DIN 6340: thick, wide, hardened; for clamps and slotted holes.
DIN 125: thin general-purpose flat washer, often soft.
DIN 6796: conical spring washer that keeps preload in bolted joints.

Common problems

Soft washer dishing into a clamp slot: use the hardened DIN 6340.
Burr side up: these are blanked and not deburred, so put the smooth side against the nut.
Forgetting thickness in the stud length: add s to the stack.

FAQ

What is a DIN 6340 washer?

A thick, hardened, wide washer for clamping devices such as strap clamps on machine tables. It is mainly used over elongated (slotted) holes.

How hard are DIN 6340 washers?

The catalogs we checked list heat-treated steel at 350 + 80 HV 30, phosphate finished, blanked with edges not deburred.

Why is there no M14 size?

Some catalogs sell a DIN 6340-15 (M14, 15 x 40 x 5), but the catalogs themselves note that size 15 is not on the official standard sheet, so we left it out.

How is a DIN 6340 washer ordered?

By bore d1, for example DIN 6340-17 for an M16 stud.

Can I use a DIN 125 washer instead?

DIN 125 washers are thinner, smaller and usually soft. Under a strap clamp over a slot they can dish. Use DIN 6340 for clamping.

Is DIN 6340 the same as DIN 6796?

No. DIN 6796 is a conical spring washer for bolted joints. DIN 6340 is a flat, thick, hardened clamping washer.

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