Scanned with an Artec Eva, this is a cast aluminum housing designed to hold a par36 (4” round) sealed beam lightbulb. These are found in most of the beacon and lightbar products from Federal Signal that were sold in the late 60’s through the 70’s. Some of the models that used these include the Model 11 Visibar, Twinsonic, Aerotwinsonic, Model 14 beacon & Model 184 beacon.