This is a master snoot, with 4 leaves that have progressively smaller diameter holes. Each leaf may be placed in front of the master snoot, resulting in different amounts of light concentration. This 5-in-1 snoot fits the Mole Richardson 10" Junior Fresnel.
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.