A total re designed swinging arm frame was introduced in 1959 fitted with the 175cc engine first seen in the D5 model. Arguably the most popular of the bantam models the D7 production ran from 1959 to 1966 with various derivatives of the model being produced, the later bikes being fitted with a separate ignition switch and remote battery coils system.
Some confusion can occur between the last of the GD7 models produced in 1966, BSA re used the same frame number sequence as they used on the early 1959 bikes. All the engines were stamped with GD7 but not the frames so you can have two D7 machines with identical frame numbers.