Odd plate - Vintage car?

[Restoring Your Finds]

Hello all,

Was out last weekend and found this. Have no clue what it can be. All I can think of is some part of an old car. All letters can be easily read and the Co at the end probably stands for Company. I can't figure out exactly the order of the other letters : EMRT...? Diameter is 4 inches. Probably not the find of a lifetime but I would still like to know what it is.

Any help is welcome !