Four foot wooden arms were introduced by the GWR in 1887, and used for new installations and renewals until the advent of steel arms (S0015/1) in 1930. They are suitable for wooden posts and dolls up to 26′ tall. The occasional lattice or concrete post was also found. Signals above 26′ used a 5′ arm, and this is the subject of a separate pack. The wooden arm is now thought to be extinct on Network Rail as the GWR and BR(WR) replaced many with steel arms, and eventually replaced the whole signal with the tubular steel post type.