Mounted on sensitive spindle 1, which bears against workpiece a being checked, are two disks, 2 and 3 , held by spring 4 to the locating flanges of spindle 1. Upon displacement of spindle 1 disks 2 and 3 make contact with either of contact pins 5: with the top contact pin for oversize workpieces a, with the bottom pin for undersize workpieces and with neither for within-size workpieces.
$473$SL,M$