We have a Thermostat Cover Vintage Salvage.  It may be bakelite, I'm not sure.  It is black with a clear plastic round cover.  I'm not certain if the actual thermostat held the cover in place but it is loose and if wanted to use it on the piece a spot of glue on the rim would hold it in place.  It could be bakelite I'm not certain, it dates somewhere between the 1950's - 1970's.  The round which would go against the wall measures about 4" across the center with the plastic clear round measures about 2 5/8" across the center.  There is a scuff mark on the clear round.  I thought someone could re purpose this piece...