What is a Mid Size Box Plate and is this one?

[OutBack Duo]

I found both of these plates on the same day in the same yard. They are either copper or brass on the front and lead on the back. Someone told me that the smaller one was a medium size box plate and that they are very rare.

My questions are:
is it a Medium box plate?
how rare are they?
how much would it be worth if I were going to sell it?

I am not thinking of selling it but when people see it they always ask what it is worth.

 

[snake pit]

I think it is a Keggereis Oval Box Plate, They had it valued for $285.00.
Those are two nice pieces

 

[snake pit]

The other is a US oval belt plate Belt Plate. It is valued at between $200. To $600..