Compresses valve springs for quicker, easier camshaft, valve seal, valve spring or retainer service-because you don't have to remove the head from the engine first! It's an OEM-approved tool that you use with a 3/8" ratchet or breaker bar. Works on: 1991 and newer Ford 4.6L, two valve, V-8 engines; and 1997 and newer Explorers with 4.0L engines.