An O-ring is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a disc-shaped cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface..
.A strainer is a perforated (punched holes) metal part used in household water systems to strain or filter out debris in the water system, sink, or shower/bathtub.