The Rotur Double-Ended Caliper can be used with workpieces up to 7 inches in diameter. To get precise dimensions of your workpiece, simply measure the exposed end whilst the other is still in contact with the work.  For repeatable measurements, the calipers' position can be locked by tightening the adjuster screw. The ends of the calipers won't scratch the workpiece because they are rounded. SKU: CDE7