The patented automatic self-centering action of these jigs assures accurate center drilling every time, even on round objects. Large steel clamping screw tightens the tool like a vise, with rugged aluminum sides holding work securely without damage to the wood. Large 2″ to 2-7/16″ capacity on all models will handle most size requirements. Drill guide centers are hardened, guide holes are precision drilled and reamed for extreme accuracy. USA.