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This is a set of 36x 2-aspect 1/76 scale small call-on signal heads representing those made by GRS for the GWR 1930s colour light signalling in Bristol and Paddington. It is typically found on gantries and brackets to signal minor movements where the long distance visibility of a standard (typically searchlight) head is not required.
There is a 2.5mm hole in the bottom to facilitate pole mounting and there is space to fit two 1.8mm LEDs which are typically red at the top and green at the bottom.
These heads have a rounded bottom on the backplate which can be cut off to represent the flat bottom variant.