This is a standard 3 Inch tri-clover clamp that folds into three pieces.

It is an uncommon size in the beverage industry as most fittings jump from 2" to 4" pretty quickly. For example our 50L kegs at 2" jump to 4" on the Kegmenters.
This particular size is suited for FermZilla Tri-Conicals and PolyPhoenix fittings.

They are often used on brewery hardware larger than 100L in size or used on prestige brewing equipment.