These Big Block Chevrolet seat spacers are .300″ thick and have a 1.732″ O.D. They fit springs with a 1.468″ O.D. and 0.630″ I.D. Late model Big Block Chevrolet engines are originally equipped with exhaust valve rotators. Until now, the only way to make up for the rotator was to stack .300" of shims under the spring. This was sloppy but also did not fit as well as these seat spacers. These will locate the spring with an outside step so the spring cannot “walk” around on the head.