MANFROTTO 521SB
The Manfrotto 521SB Remote Control Splitter Box allows you to connect two remote controls from the 521 series to control the camera with both hands. This means you can control the zoom with one unit and the focus with the other, handling them with one hand each.

The 521SB has a 3/8" and 1/4 - 20" thread and is supplied with a butterfly screw to mount it directly on the 595B Fig Rig crossbody.