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 49mm (7′) wide x 38mm (5’3″) deep; the trimmers are each 73.5mm (10′6″) wide x 5.5mm (9″) deep. There are two of the trimmer frets shown in the photo in each pack. Three ground signal arms are also included. The parts are etched in 0.018″ brass.
To model a complete signal as shown, you will need: a base post (S07); dolls (S7/33 series); signal arms (S7/04 LNWR lower quadrant or S012 series LMS/BR upper quadrant); post caps (SC010); lamps (SC030 lower quadrant or SC011 upper quadrant); and a ladder (S7/09 series).