The Sunwayfoto DDY-64 Disc Clamp is a circular Arca-style clamp that fits to just about any 3/8"-16 or 1/4"-20 threaded screw (a 1/4"-20 adapter bushing is included to convert the 3/8"-16 thread). An integrated bubble level allows you to ensure that your camera's position hews to the horizon.
With a diameter of 2.5", the DDY-64 fits many brands of ball heads, such as those from Arca-Swiss, Jobu, Really Right Stuff, and more. The clamp fits most Arca-style dovetail camera plates (plate and head not included). With the provided 6mm Allen screw, you can remove your head's existing clamp and replace with the DDY-64.