Made of high quality steel, durable. Six telescopic gauges with different specifications can be used to quickly measure the inside of the hole. Under the uniform spring tension, the plunger of the measuring tool expands from the center to the diameter or groove width of the hole to be measured, and then locks it in place with the knurled knob. The hole size can be obtained by measuring two contact points with a micrometer or caliper. Telescopic gauge is used to measure the inner diameter or internal through groove of the machine by comparison . Portable and practical, easy to operate. Name:telescopic gauge Quantity:6pcs Colour:Silver Material:steel Size:8-150mm(5/16inch-6inch) Package Contents: 1 * 1/2inch to 3/4inch gauge 1 * 2-1/8inch to 3-1/2inch gauge 1 * 3/4inch to 1-1/4inch gauge 1 * 3-1/2inch to 6inch Gauge 1 * 5/16inch to 1/2inch gauge 1 * 1-1/4inch to 2-1/8inch gauge Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.