This is a 2-Leaf Barndoor Set with built-in filter/diffuser holder for the Mole-Richardson Molepar 9 light bank.
Barndoors narrow the beam 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.