The rings on this Flush Ring Style Brass Knobs are flush to the surface. Knob measures 1-3/16 inches (30 millimeters) in diameter and extends 1-9/16 inches (40 millimeters) from the door surface. Knob is made of solid brass, in your choice of six color combinations. The knob can be used on glass door thicknesses from 1/4 to 1/2 inches (6 to 12 millimeters). Hole size required for is either 3/8 or 1/2 inch (10 or 12 millimeter) in diameter.