Very useful tool for installing a piston into a cylinder. Everyone has been there juggling the piston as well as the rings which are under tension and it becomes more a game of patience than anything else. This tool keep the rings pressed in as the guide is slid into the bore of the cylinder and the piston is pushed all the way into position to allow for the gudgeon pin to be installed. Job done. Suitable for pistons from 40-85mm diameter.