This base has all the tilt, turn and rotate control features of the Standard Base, but it's only 2-1/2" (63.5mm) high. Designed for working close to the bench surface. When used with the 304 Low-Profile Head, it allows the work to be swung out and away from the bench surface. This base has three 1/4" (6.3mm) countersunk mounting holes on a 4-5/16" (109.5mm) bolt circle for attaching directly to a work bench or to a portable Base Mount. Accepts all 5/8" (15.9mm) stems.