The spring and the rubber jaws grip the glass, automatically freeing your fingers and wrist to do faster and more accurate projects. The glass is held firm by the spring pressure, allowing more force into the grinding wheel, thereby, speeding up the grinding operation. A circular pivot base makes it easier to generate a non-straight configuration on the edge of the glass, without snagging on obstructions on the surface of the table (such as loose glass splinters. Use replacement jaw pads Cat. No. 205121.