North Stafford Railway Wedge Type
Described by Keith Neal in his excellent and unique book, Searching For Railway Telegraph Insulators, as being used by the North Stafford Railway (NSR), the wire passed through the groove and was retained with a loop and 2 wooden edges. It was stated as being a more secure, faster fitment than by conventional means.
Jim Gough, a fellow collector, provided me with these images, though they do not capture the heaviness to be found with this insulator upon actual handling. Similar in height and diameter to a Pothead and other than the slot, a thread hole and short inner skirt they are completely solid and of a cream porcelain suggesting it originated from a UK factory.
The text, though similar to that seen on several Sinclair-Aitken examples, does not tell us who made this type of insulator. The Patent number though obviously 1412 has no direct link that I can find.
The underside offers no clues to its origin either. The thread is a standard thread and size as found on most Cordeaux Standard Line and Pothead insulators