Not only CLASS IV but Registered I'm sure by someone unaccustomed to the correct Board of Trade procedures - but why register this in the ceramics CLASS is a mystery, can't imagine they were concerned about industrial espionage.
Thomas Dawkins not, of course, the maker of this item, but presumably felt the need to be able to offer their musically minded customers insulators on which to stand their pianos - "buy a piano guv. and we'll throw in a gorgeous set of insulators".
This is quite a chunky piece, and unusual insofar as it does have its own Rd. No. - I can't imagine there are many British made insulators with such a feature - trade marks, but not Nos.
I say British, but for all we know (cue for a song) this might have originated on the Continent somewhere - or am I wrong and piano insulators are a peculiarly British invention that didn't spread beyond our shores?? I've looked under miscellaneous on Pamela's Pressglas-pavillon site but can't see any examples. Is anyone aware of known examples categorically made outside the U.K?