The Ceramic Shop calipers are made out of durable acrylic held together with quality hardware. These calipers are ideal for measuring perfectly fitted lids for thrown or hand-built pieces. As you measure the inner rim of your piece, the opposite end of the callipers automatically determines the appropriate measurements for your lid. An adjustable wing nut allows you to secure the arms of the callipers to specific measurements. This tool is indispensable when creating any ceramic forms designed to fit neatly together.