Watch Gaskets "O" ring seal for case back, Diam up to 40mm, thick 0.5mm to 1mm
£2.49
The smaller gasket will stretch and won't "slacken out" when you close the back. Zenith 200M diver's watch - case No. 19.0130.393. 30 x 1mm. you can use size 32mm and stretch it manually to the size required then.
