All the top race crews know that minimizing piston ring friction to the lowest amount before blow by is one of the best ways to maximize engine efficiency. This tool accurately measures the pull of a ring in the bore. This is the ultimate tool for quantitatively measuring friction as a function of gap and diameter. Get it right, and get the trophy! The kit includes two expandable platforms for pulling, and a precision digital gauge for accurate readings. Tool fits ring bore diameters between 2.377"-6.25". Detailed instructions included. U.S. Pat. 8,479,570