Plastic hood with bayonet attachement. Is designed for lens with 58mm filter thread that has a bayonet mount for the hood on the outer side of the barrel. I assume for Tamron or Sigma, but not sure which lens. Measures approx 67mm diameter at lens end out to 83mm at other end, length 82mm. Fits over the Olympus 40-150mm and if the bayonet was the same style would attach and work well.