This is an articulating arm with an O-ring focusing rack with 3" diameter, and clamp for stereo microscopes. Great for examining parts attached to a larger or awkward shaped item, this articulating arm stand comes with a clamp that can be secured to ledges up to 2 1/8" (53mm) thick. Features & Specifications: 3" (76mm) O-ring Focusing Rack INCLUDED BY DEFAULT 3-1/4"(83mm) O-ring available UPON REQUEST ONLY 40" (1020mm) Reaching-out Length 20lbs (9kg) in Weight A Versatile Articulating Stand with Clamp for Covering Large Working Area Articulating Design for Flexibility Manufactured under ISO 9001 Quality Control Standard Excellent Five (5) Year Factory Warranty Unbeatable Low Price Guaranteed or the Difference Back! Satisfaction Guaranteed or Your Money Back! Packing List: One Articulating Arm with Clamp One Focusing Rack w/3" diameter (unless otherwise requested by buyer) User's Manual