This is a Interfit Honeycomb Snoot reflector for Stellar and Venus S-type accessory mount monolights. It's compatible with Stellar X, XD and Xtreme as well as Venus flash heads. The snoot produces a 20° narrow beam of illumination ideal for use as an hair light.
Use of a snoot will result in a small circle of light, when it is attached to the front of your light source. The size of the circle of light will be determined by the opening of the snoot, its length, and the distance of the subject. Consider them as a painter would a brush, or a sculptor would a knife, or chisel.