Most high performance engines today require the use of larger-than-stock diameter valve springs. This 1.320 inch Spring Seat Cutter for installing larger springs and hardened spring seats on GM Vortec Heads will allow the engine builder to machine the cylinder head to the proper size for your spring. Each cutter requires the use of an arbor/pilot, which are available in three different sizes. 1.320 inch O.D. .630 inch Cuts Guide