This is a Photogenic Adjustable Iron Counterweight, which will slide onto any open-ended light stand leg or boom arm whose diameter is between 7/8, and 1-1/8". This 3.4 lb (1.5kg) counterweight locks into place with a twist of its screw key.
What's in the Box
Photogenic
Adjustable Counterweight for Boom Arms - 3.4 lbs (1.5kg)