Our most popular base! Accepts all 300 series Heads and the PV Jr. 203 Head or any 5/8" (15.9mm) diameter shaft. Create a versatile work holding system by selecting two or three different Heads! Single control knob and exclusive "split-ball" lock Head firmly in place Base features 4.3125" (109.5mm) bolt circle countersunk for three 1/4" (6.3mm) flat-head screws (not included) Height: 3.75" (95.2mm), Weight: 1.4 lbs. (0.6kg)