A circular item, usually having a flat or grooved flange, bos (es), and/or counterbore designed to accommodate the end of the spring. It is used to position the spring, but does not encase the spring or restrain lateral motion. It may be used in conjunction with a retainer, helical compression spring. Excludes washer (1), (as modified) ; seat, ball socket and holder, spring. See also rotor, engine poppet valve.