Sun dial? Lock hole thing? Numbered.

[MackDigger]

I haven't posted in a while but this one really has me stumped. It's really nice lookin. And has a number/letters on the back but I can't find anything. Any guesses or help is appreciated. Thanks.

 

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[Anduril]

Maybe a peephole for a firebox?
Like on a steam locomotive, or anything that burns wood, coal, etc.. - even a commerical oil-burning furnace, I suppose.

I think the the hole is too large to be a security peephole.

BTW: Definitely not a choo-choo train guy here.
I'm almost positive the device I'm thinking of is NOT called a "firebox peephole", but I'll let someone else chime in with the Rail-Roaders' official jargon.
Oh, and my guess could be way off.

 

[Breezie]

I agree with Anduril in that it is a Furnace Peephole.

Neat find
Breezie