For all 3/8in and 7/16in Rocker Studs. Remove valve spring from an assembled engine for checking or replacing quickly and easily. Press down to compress coil spring, then remove valve keepers. Release slowly.Proform On-Engine Stud Mounted Model for 3/8 and 7/16 Studs 66784Specifications: Feature/Benefit For all 3/8 inch and 7/16 inch Rocker Studs. Tool Type Valve Spring Compressors Category Spring Compressor Description_ABR Spring Tool Description_SHO Spring Compressor Description_INV Valve Spring Compressor Description_INV Stud Mount Description_DEF Engine Valve Spring Compressor Description_ASC Valve Spring Compressor Description_ASC On-Engine Stud Mounted Model for 3/8 and 7/16 Studs Description_LAB Valve Spring Compressor Description_LAB On-Engine Stud Mounted Model for 3/8 and 7/16 Studs Description_DES Valve Spring Compressor Description_DES On-Engine Stud Mounted Model for 3/8 and 7/16 Studs Description_EXT Engine Valve Spring Compressor Description_EXT On-Engine Stud Mounted Model for 3/8-24 and 7/16-20 Thread Rocker Arm Studs Description_EXT Use with Valve Springs Up to 700lbs Description_EXT Made from High-Quality Steel Material Description_EXT 9 Inch Handle with Rubber Grip Description_EXT Sold Each Description_MKT For all 3/8in and 7/16in Rocker Studs. Remove valve spring from an assembled engine for checking or replacing quickly and easily. Press down to compress coil spring, then remove valve keepers. Release slowly.