Stage Equipment & Lighting
Manfrotto 123 Super Boom Pivot Clamp
Manfrotto 123 Super Boom Pivot Clamp, Boom Clamp, Pivoting, For use with all super and heavy duty booms, For boom shafts with a diameter of 35 mm, Combi tripod mounting spigot 1-1/8" (28 mm) and 5/8" (16 mm) attachment
https://www.bizrate.co.uk/stagelightingequipment/manfrotto-123-super-boom-pivot-oid5363001492.html