Green’s Dictionary of Slang

screwdriver n.

1. (Aus./UK prison) a principal officer who ‘drives’ his subordinates [screw n.1 (2c)].

[UK](con. 1920s) J. Sparks Burglar to the Nobility 84: In rushes the screwdriver — the chief screw — and yells us all uop to our feet.
[Aus]Tupper & Wortley Aus. Prison Sl. Gloss. [Internet] Screwdriver. Chief prison officer or superintendent.

2. the penis [screw n.1 (1b) + pun].

[US]Maledicta IV:2 (Winter) 194: The engineer [is represented] with his derrick, screwdriver, rogering iron, piston and pumphandle.