Indexing accuracy up to +4 arc sec. Repetitive accuracy of +1 arc sec. Minimum indexing degree is 10 and 50 High accuracy and high rigidity Precision Dual Lead Worm Gear System. High accuracy and high rigidity three pieces Hirth Coupling Gear with robust clamping structure. Wear resistant worm wheel: ALBC4 grade, HRB180 hardness. Does not float during degree indexing. Concealed water proofing structure. High rigid and gripping greatly increase efficiency effect during heavy cutting.