This device is used to verify the  inside diameter of paper and cardboard tubes using a series of brightly colored rings, each representing a different inside diameter size range. The plug is inserted into the end of a cardboard tube or roll of paper, and the width is indicated by the color of the ring exposed. This instrument operates using a “pass/fail” procedure. Green is passing, Yellow is acceptable, and Red is failing. Model CPG – 6 is designed for cores ranging from 1 -1/4” to 1-3/4” inside diameter. Other diamters are available upon request.