The speedring is specifically designed to fit both rectangular and octagon standard softboxes from Fotodiox. This speedring has an outer diameter of 7-5/8" (19mm) and fits 1/4" (6mm-7mm) standard rods. By replacing the insert with a different model, you can mount the softbox on almost any strobe, allowing you to expand your lighting options or use the same softboxes for multiple setups. Features: Standard Speedring for Rectangular or Octagon Softbox or Beauty Dish All metal design, Rotation Ring with Thumb Screw Lock Speedring has an Od of 7-3/4" and Id of 6" Insert has an Outer Diameter of 5-7/8" 24 Month Manufacture Warranty Product Speedring Plate & Speedring Insert for Select Strobes Plate Outer Diameter 7-3/4" (19.7cm) Plate Inner Diameter 6" (15.2cm) Rod Diameter 1/4" (6mm) Insert Outer Diameter 5-7/8" (14.9cm) Manufacture Fotodiox Inc. Warranty 24 Months