Quickly measure everything from diameter, to grooves, to hard-to-reach recesses with the PROFORM Telescoping Gauge Set. Simply insert the gauge (six sizes to choose from) into the area and turn the knob. The spring-fed arms will snap to outer edges. Now, tighten the knob to lock the inside measurement. Comes with six gauges ranging from 5/16" to 6" and a durable carrying case.