I found this piece in a large collection I bought a few weeks ago and never really knew what it was until I got it home and cleaned up. This is a CD 106 Hemingray RDP Pat date that is unlisted, the only one listed is the [320] index embossed with "PATENTED" with RDP, this one is embossed [250] index only "PATENT"and as far as the guide goes, there is no RDP [250] index. Shown is the base shot, all drips are exact in height, shape and size indicating that this was not just an underpoured mould but a different drip baseplate used. Really is neat when you find an insulator that people say isn't supposed to exist!