Fotodiox Softbox Speedring (Insert and Base Plate) for Profoto Compact Lights series D1 250 W/S, D1 500 W/S, D1 Air 1000 W/S, D1 Air 500 W/S, Pro Series Acute B 600 W/S, Pro-B 12000 W/S, Acute 2-D4 Strobe Light All Metal Design, fits standard 1/4" (6mm -7mm)rods. Standard Speedring for Rectangular or Octagon box Rotation Ring with thumb screw lock Smooth surface for effortless mount 24 Month Manufacture Warranty