From Manufacturer
The Manfrotto Ezybox Quad Bracket is an ideal way to quadruple your shoe-mount flash power or shorten your recycling time. Mount up to 4 shoe-mount flashes and add an Ezybox Studio Softbox or umbrella for studio quality on the go. You can hardwire your flash units via the included PC and 3.5 mm (mini) cables or utilize one of the many optional radio triggering systems to avoid a tangle of wires. The Quad bracket is compatible with the Nikon SB-900.