This is a single-arm heavy duty boom for stereo microscopes. The diameter of the holding ring is 3" (76mm). This rugged boom stand weighs about 40 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 24" Overall Length. 16" Single Arm. 17" High Pillar 9" x 9" x 1-3/4" Solid Cast Steel Base 40 lbs in Weight