Ergotron LX Sit Stand Collar Kit Add on for Desk Monitor Arms Polished Aluminum

Amazon

Allows a second LX Sit-Stand Arm to be attached at any point on the pole of an installed base Simple installation Easily reposition height on pole by loosening/tightening collar's set-screws Package weight: 0.1323 pounds

Zoro Tools

Ergotron LX Pole Collar. Weight: 45 g. Package weight: 200 g