gsg vernier maste are used to calibrate and set vernier calipe. the master is superior to gage block calibration because they do require block stacks and therefore it is much faster to the ipect linear range of the tool. in addition they indicate wear on the caliper anvils because both the id and od jaws are ipected without additional setup. model # vc-1e (english) model # vc-1m (metric) 1.00-6.00 diameter in 1.00 increments for outside jaws, 1/2 to 4 1/2 iide jaws. +/-.0002, 25-150mm diameter in 25.0mm increments for outside jaws, 12.5 to 112mm for iide jaws +/-.005mm case hardened, stabilized, ground and lapped to +/-.0002. larger sizes are available upon request.