Specifically designed to eliminate mistakes during insulating glass unit fabrication, the CRL Metric Insulating Glass Caliper makes it easy to measure I.G. unit thickness in sliding windows and doors. This useful tool features 101.6 millimeter (4 inch) scale on each side for quick and convenient calibrating. Made of high impact resistant plastic for durability. An inexpensive way to measure insulating glass units or any other object where thickness dimensions are required.