This is a 3D double-arm heavy duty boom for stereo microscopes. It allows you to turn microscope head around three different axis (x, y, and z), allowing you to point the microscope head in ANY direction you wish. The diameter of the holder ring is 3" (76mm). This rugged boom stand weighs about 60 lbs. It is an ideal stand for gemologists, collectors, engravers and engineers in industries. This stand is brand new in box. Features & Specifications: 3" (76mm) Holder Ring 30" Overall Length 20" Double Arms 17" High Pillar 10-1/4" x 8-1/4" x 2-0" Solid Cast Steel Base Shipping Weight: 55 lbs