The DCA-1 installs onto most digital, dial, or vernier calipers and features protruding contact points that allow measurement of the center of the braking surface rather than the unworn edge of the rotor for a more accurate measurementThe conical end points of the DCA-1 can be used to measure center-to-center distances of bolt holes for calculating bolt circle diameter (BCD) of chainrings and cranksCaliper AccessoryClearDCA-1UPC/EAN/GTIN: 763477002389