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Sealing Ring Dimensions (DIN 7603 Form A, 8 to 48 mm)
Guide · Updated October 28, 2026
DIN 7603 covers flat sealing rings; this chart lists Form A from 8x11.5 to 48x55. Values agree across HBS Solutions and the Ganter / J.W. Winco catalog. Check your supplier for critical work.
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Step by step
- Match the thread: The nominal inner size matches the plug thread: 14x18 fits M14x1.5, 21x26 fits G1/2.
- Check the collar: The outer d2 must sit inside the plug collar and on a flat port face.
- Pick the material: Copper and aluminium crush to seal; steel rings are for higher temperatures.
- Use once: Fit a new ring each time the plug is removed.
DIN 7603 Form A sealing ring dimensions (mm)
Columns: nominal size (inner x outer), actual inner diameter d1 (+0.3), actual outer diameter d2 (-0.2), thickness s (±0.2).
- Size | d1 | d2 | s
- 8x11.5 | 8.2 | 11.4 | 1
- 10x13.5 | 10.2 | 13.4 | 1
- 12x16 | 12.2 | 15.9 | 1.5
- 14x18 | 14.2 | 17.9 | 1.5
- 16x20 | 16.2 | 19.9 | 1.5
- 17x21 | 17.2 | 20.9 | 1.5
- 18x22 | 18.2 | 21.9 | 1.5
- 20x24 | 20.2 | 23.9 | 1.5
- 21x26 | 21.2 | 25.9 | 1.5
- 22x27 | 22.2 | 26.9 | 1.5
- 24x29 | 24.3 | 28.9 | 2
- 26x31 | 26.3 | 30.9 | 2
- 27x32 | 27.3 | 31.9 | 2
- 30x36 | 30.3 | 35.9 | 2
- 33x39 | 33.3 | 38.9 | 2
- 42x49 | 42.3 | 48.9 | 2
- 48x55 | 48.3 | 54.9 | 2
Worked example: M20x1.5 drain plug
An M20x1.5 plug takes a 20x24 DIN 7603 ring: 20.2 mm inside, 23.9 mm outside and 1.5 mm thick. It sits under the 25 mm collar of a DIN 908 or DIN 910 plug.
Common problems
- Still leaks: the ring was reused and already work-hardened; fit a new one or anneal copper.
- Ring sticks out past the collar: the ring OD is too big for the plug; check d2 against the collar.
- Ring cuts or splits: overtightened, or a steel ring used where copper was needed.
FAQ
What is DIN 7603?
The standard for flat sealing rings (crush washers) used under screw plugs and banjo fittings. Form A is the plain flat ring.
Why is the actual size different from nominal?
The ring is made slightly oversize inside (+0.2 to +0.3) and undersize outside (-0.1) so it centres on the thread and fits the collar.
Which ring fits which plug?
The nominal inner size equals the thread size: 10x13.5 for M10x1 or G1/8, 27x32 for M27x2 or G3/4. Check against the plug collar d2.
Why no 4, 5 or 6.5 mm rings?
Only one source lists them, so they are left out.
Related guides and calculators
- Socket screw plugs (DIN 908)
- Hex head screw plugs (DIN 910)
- Light screw plugs (DIN 7604)
- All free machinist calculators
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