Above:  Paasche F from the 1950's.

Close-up of Paasche D-D. The needle can be controlled by the trigger. You can see the rod (red arrow) that moves the needle protruding from the front of the body and into the needle assembly.

Paasche D-D (top) and H2 of the same era. The difference is that the D-D is a double action meaning the amount of paint can be controlled from the trigger. On the H it's done manually by adjusting the tip.