The Edelbrock Sure Seat Valve Spring is designed for use with non-rotator style retainers. It is made of the highest quality spring wire and precision-wound to precise specifications. The basic purpose of a valve spring is to close the valve while also ensuring that the valve train stays in contact with the cam lobe. Edelbrock's sure seat valve springs are designed for use on OEM (Original Equipment Manufacturer) heads when used in conjunction with their Performer-Plus, Performer RPM, and Torker-Plus camshafts. The valve spring seats provide protection for aluminum heads and locate the valve spring to prevent it from moving around at higher engine speeds. Good valve springs provide adequate seat pressure to allow a tight fit between the valve face and the valve seat to seal the combustion chamber. Valve springs requires checking the clearance between the rocker arm and the retainer before starting the engine. The inside diameter (ID) of the inner and outer spring is 0. 875 and the outside diameter (OD) of the outer spring is 1. 222.