Several versions of the cone type exist, though none within the collection. They are usually corrugated but earlier versions have smooth sides.
Usually located on the top of a telegraph pole, they were, by the very fact that there was normally only one per pole, very scarce.
W.Keith Neal, in his book, Railway And Other Rare Insulators, states that, to his knowledge there are four distinct patterns, marked Patent No.s 1,2,3 and 4.
Fuller & Son
Inverted cone insulator marked 'Fuller & Son, Bow, Patent No.2' as portrayed in 'Searching for Railway Telegraph Insulators'. Found between Wimbledon and Raynes Park in 1921 by W Keith Neal.
The original inverted cone, stamped 'Fuller's Insulator'. This is believed to be the prototype of the inverted cone and as such did not have a patent number assigned.
A smaller prototype version, approximately 1/2 size of the previous version.
Fullers Patent No.4, consisting of five sheds made from a total of two pieces
Images from W Keith Neal's books 'Searching for Railway Telegraph Insulators' and 'Railway and other rare Insulators'
Tris Horton has found his first piece of what is believed to be a Fullers Cone no.2. Excellent news Tris, now for a bit more.
The piece looks very similar to a Fullers Corrugated insulator as depicted on the Corrugated page and as such made me sceptical. Tris responded my measuring the sample and mounting it vertically which confirmed it definitely sloped inwards and could only have come from a cone type insulator.