Waterproof Your Watch Again - These watch seals are made of solid tube rubber to create an airtight seal and are flexible enough to fit different shaped case backs One Set Fits Most - Set of 19 sizes. These assorted sizes o-ring gaskets fit a variety of watch case backs in diameter from 12 mm to 30 mm/0.47 inch to 1.18 inches; Allows watchmakers and others who work on watch case backs to select exactly the o-ring gasket they need Measuring Tips - Measure the outside diameter of the inside lip on the gasket, where the old gasket was seated; Be sure to select a gasket that is point-one millimetre smaller in diameter than measured to ensure a tight seal; Should use a digital gauge Sizes: 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 and 30 mm/0.47, 0.51, 0.55, 0.59, 0.63, 0.67, 0.71, 0.75, 0.79, 0.83, 0.87, 0.91, 0.95, 0.99, 1.02, 1.06, 1.10, 1.14 and 1.18 inches Package includes: Watch Back Round Gasket x 950 (50 pieces x 19 sizes, other accessories are not included)