The O-Rings are used in static applications or in dynamic applications where there is relative motion between the parts and the O-Ring. Dynamic examples include rotating pump shafts and hydraulic cylinder pistons. O-Rings are available in various metric and inch standard sizes. Sizes are specified by the inside diameter and the cross section diameter (thickness).These include the O-Ring with an x-shaped profile, commonly called the X-ring, Q-Ring, or by the trademarked name Quad Ring.