For use with four- & five-bolt chainring patterns, this highly accurate gauge measures in millimetres for the most precise reading. The piloted tips on each of the tools arms are inserted into the chainring holes, chainring bolts or crank holes, measuring the distance between the two points to determine the exact chainring size for your specific frame. The measurements are read on a laser engraved scale on the anodised aluminium gauge face, with additional pattern measurements referenced on the included mounting pattern chart. A convenient tool to use when thinking of replacing your chainring, the Chainring Diameter Gauge CDG-2 is a brilliant precision workshop tool from Park Tool.