The Starrett AccuBore is a high-quality, trigger-activated, three-point contact bore gaging system with extended range. Its convenient single-hand operation provides speed and control. It also features an easy-to-read digital display as well as mechanically-driven parallel anvils which extend simultaneously, establishing a more true alignment to the axis of the bore, providing consistent pressure and more accurate readings as opposed to models with spring-driven contacts. The gage also features a set of "go/no go" lights that quickly indicate whether a bore measurement is within a preset tolerance window. Pistol Grip, 3/8-1/2" (10-12.5mm) Range window.