I designed this ratchet screwdriver to be adaptable for all 6-Kant 1/4 of inch bits.
The bit rotation is locked while unscrewing and for screwing the spring provides a torque control.
The maximum torque depends on the spring stiffness and on the length of the spacer. To adjust the maximum torque for screwing I also included a M5 nut in the back of the handle that allows to increase the torque screwing on the back of the screwdriver a M5 bolt (This part is optional).
The ratchet is a single piece that have to be printed twice: one for the head of the screwdriver (have to be inserted in it) and one moving with the spring.
I used a spring of 6.5x18mm, if you have a spring of a different lenght just modify the spacer length on CAD file.
I used PLA, but probably it is better to use ABS for ratchet part in order to have a better strength
Designed using Onshape