R-341 Square O-Ring (ID: 3 1/2", CS 3/16", OD 3 7/8"), 8PK The o ring is placed into a groove to secure them in place, and then compressed between two surfaces..
R-221 Square O-Ring (ID: 1 7/16", CS 1/8", OD 1 11/16"), 16PK The o ring is placed into a groove to secure them in place, and then compressed between two surfaces.