The Hensel 4 Leaf Barndoor Set with Filter Holder for 7.0" Reflector fits the #504 grid reflector. Barndoors are designed to create a narrow beam and spread of a light fixture. They help create a 3-dimensional look to a lighting scheme by placing light in a specific area, or by keeping it away. The more leaves a barndoor set has, or the longer the leaves the more precisely the beam can be controlled.