This style of 3-doll bracket (called S61) was introduced by the London & North Western Railway in 1883. The components were also used in offset signals and larger arrays. The design was continued by the LMS until the advent of tubular steel posts in the 1930s.
The brackets are 28mm (7′) wide x 21mm (5’3″) deep; the trimmers are 64mm (16′) wide x 4mm (1′) deep.
The parts are etched in 0.015″ brass.
To model a complete signal as shown, you will need: a base post (S0017); dolls (S0033 series); signal arms (S004 LNWR lower quadrant or S0012 series LMS/BR upper quadrant); post caps (SC0010); lamps (SC0030 lower quadrant or SC0011 upper quadrant); and a ladder (S009 series).