This pattern of signal arm was introduced by the GWR in 1887, and was used for new installations and renewals until the advent of steel arms (S015) in 1930. Note that the 5′ arms are for use on posts greater than 26′ tall.
The actual size of the fret is 143 x 93½mm; it is etched in 0.015″ brass.
To model a complete signal, you will need: a wooden post (S06, S017 or S028); a finial (SC05); a lamp (SC04); a balance weight (SC041/1); a ladder (S09 series or S7/09); and a platform (S7/02/1). A very few signals had a lattice post (S7/02, S7/02/2).