This is a 4-Leaf Barndoor Set for the Altman 1200SE, 1000S, 2000L Fresnels.
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.