Diamond coring motors are used with Vac-U-Rig® and Dymorig diamond core rigs to drill holes into reinforced concrete. This 15 amp model provides core drilling power where 20 amp service is unavailable. This unit has a 375 rpm or 750 rpm operating speed. The 4090 uses a shear pin to protect gears and motor against overload. Shear pins are easily replaced and extra pins are included with the unit. This unit will handle core bits from 2 1/2 inches to 8 inches in diameter.