A handy workshop time saver that makes determining the bcd of a crank or ring a cinch simple to use just put the pegs into the mounting holes or chainring bolts of the crank or ring you want to measure and the indicator arm will highlight the correct 4 or 5 bolt standard anodized and permanently laser etched for a long life includes a centre to centre distance scale and reference chart for measuring other mounting pattern dimensions made in the usa and covered by park39s legendar