... reliably measures the thickness of the poured concrete slab of non-metal like structure,concrete,wall,girder,bar,pole,wood and ... 80mmExtension Bar:φ25×600(mm)(3 piece) Work PrincipleDJLC-A concrete thickness gauge is composed of signal transmit, connector, signal ... Due to less square connected,no plate polishedIntelligent read and auto lockup,real-time thickness display then reduced man-made ...