A piston ring compressor is necessary for the installation of pistons into the cylinder block. The compressor folds around the piston, holding the rings in their grooves and allowing the piston and ring assembly to slide into the bore without damaging the pistons or rings. A great time saving tool. Designed for professional use and fits pistons 53mm to 125mm in diameter. Manufactured from quality sprung steel with a ratchet action tension mechanism. Adjustable with a 1/4″ drive key (supplied). Quick release button.