This is a 7" school bus tail light full assembly. It is definitely not vintage, but if you have a late 1950s to 1970s travel trailer that does not have taillights and you need something that is the same diameter as the taillights of that era, this is a functional replacement that will give you stop/turn/tail functions.
If you have vintage Auto-Lamp 575 lenses, they can be mounted to this base. If you do that your lens will fit just inside the base's outer rim. It is possible that other 4-screw lenses of the same general size may also work with the base.
The base surface mounts to your trailer with four screws on a 6.25" bolt circle. It has one incandescent two-function 1157 bulb and is grounded with one of the mounting screws to the trailer.
The red acrylic lens attaches to the lamp base with 4 screws It requires a 1" diameter hole 1" deep in the center for the bulb socket and pigtail.
The heavy duty steel base is painted with black epoxy for rust prevention.