Casserole for One

Isn't this a cute little casserole?  It measure 4 3/4" across the top and 1 1/2 " deep. I don't know where the lid came from - something my mom had. But the bottom is actually part of an electrical unit. My dad was an electrician and he brought this home. On the bottom it says, "PYREX T.M. REG. U.S. PAT. OFF. MADE IN U.S.A."  Still on the bottom, near the little lip it says "LINE."

I wish I knew what service it performed. What a neat coincidence that the lid fits!