The District carried out a reorganisation of their coupling arrangements in the late 1920s so that cars became handed like the tube lines.  The air hoses were removed from below the coupler and were placed on either side of the central door but the location varied depending on whether the car was "A" end or "D" end.   "A" end cars (west facing) had the hoses immediately next to the centre doorway while "D" end cars (east facing) had them on the outer corners of the body as shown here.

The control jumper was blanked off on the north side but the busline jumpers remained in use on both sides.

In the 1930s and 40s, when many District cars were converted to air door operation and e.p. brakes, the jumpers were altered again on the converted cars so that a set of three (control, auxiliary and brake) jumpers were provided on the north side and the busline jumper was provided only on the south side of the train.  Air hoses remained unchanged.  The objective was to ensure that, whilst trains could be coupled with air brake compatibility for emergency purposes, control and power connections could not.