This is a 40° "egg crate" grid for the Westcott 12x36" strip bank softbox.
Grids are essential accessories for any lighting system. A grid alters the shape and intensity of the light output from your softbox when it is mounted on a light head. Consider a grid as a painter would a brush, or a sculptor would a knife, or chisel.
"Egg crates" are rigid, or semi-rigid. Use of an "egg crate" will result in a narrower spread of light. The spread of light will be determined by the density of the honeycomb mesh, and the distance of the subject from the light.