The Model 300 Pro was designed primarily for making tabletops from 7 inches to 52-3/4 inches in diameter. It has 184 pre-drilled pivot holes for making 184 different size circles. The Model 300 Pro is graduated in 1/4 inch increments and is calibrated for a 1/2 inch router bit. By using a 3/8 inch router bit circle diameter resolution is increased to 1/8 inch increments. It can actually make 368 different size circles by alternating a 1/2 inch router bit and a 3/8 inch router bit. The model 300 is pre-drilled for 19 different models of plunge routers. It is made of virtually unbreakable polycarbonate plastic.