PLEASE HELP ME IDENTIFY THIS OBJECT

[mountaindetector]

I recently found this piece at a sawmill/lumber yard site from the 1920's. At first I thought it might be a cover to a light from a truck or vehicle. The little posts on the inside don't have threads so I'm not sure what it went on. It measures 3-1/2" x 4". It was quite rusty when I found it but it cleaned up with electrolysis. Any help would be greatly appreciated.

 

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[Msbeepbeep]

Don't have a clue, but someone on here will know. If you don't get answers list it on the "what's it" forum farther down the forum.