Help identifying electrical component mounted on baseboard

Hi all,

This eletrical component is mounted on the baseboard of a spare room in my 1950s home. I'm trying to identify exactly what it is . It's about 2x2 inches and is mounted in a spare room. The only visible text is "42A" and google searches aren't turning up anything similar, even doing photo searches.

I'm thinking it may be a doorbell transformer but I really have no idea. I figured this was the best place to ask.

Thanks for your help!