granite surface plate 1.Hardest uniformity of all granite surface plate2.Lowest temperature coefficient, least responsive to temperature changes.3.Moisture and corrosion free, no rusting, no oiling, will not stain or discolor. 4.Practically maintenance free, fast easy to clean.5.SmoothBall-Bearing?surface.6.Resists dust and abrasives, Non-magnetic.7. 0-ledge,2-ledge