The Piston Ring Friction Pull Measurement Tool from Proform is a highly accurate and compact handheld tool used to measure the friction coefficient of a ring inside the piston bore. By measuring the gap and bore diameter as a function, the friction coefficient can be measured easily. Less friction overall provides greater engine efficiency as well as helps prohibit engine oil blowby when piston ring gap is precisely measured. The friction pull tool is sold as a kit that includes the handheld gauge with digital display,  two expandable adapters that can measure bore diameters from 2.377 in. to 6.250 in. and a foam-lined metal carrying case.