If you are replacing a mineral crystal - add 0.1mm or 0.2mm for a good tight fit. These crystals are made in Germany - very high quality and exceptional clarity.
Sternkreuz High Dome Acrylic Domed Watch Glass Crystal + Date Lens Magnifier New
Sternkreuz Domed Acrylic Crystal With Gold Tone Tension Ring 17mm to 37.2mm
Sternkreuz Watch Glass Acrylic - Slightly Domed - 1mm thick Dia 17mm to 50mm
Sternkreuz Domed Acrylic Crystal With Chrome Tension Ring 17mm to 37.3mm
BCL/Sternkreuz High Dome Vintage Acrylic Watch Glass Size 12.0mm - 36.0mm NOS
Acrylic Watch Glass Crystal Sizes in 19.0mm -40.0mm - High Domed