Gauge blocks (tseem hu ua gauge blocks, Johansson gauges, plam gauges, los yog Jo blocks) yog ib qho system rau kev tsim qhov ntev.Tus neeg ntsuas qhov thaiv yog cov hlau lossis ceramic thaiv uas tau ua tiav hauv av thiab lapped rau ib qho tuab tuab.Gauge blocks tuaj nyob rau hauv cov blocks nrog ntau yam ntawm cov qauv ntev.Hauv kev siv, cov blocks yog stacked los ua ib qhov ntev (los yog qhov siab).