This 3d-printable ratchet screwdriver is very strong, as it uses metal 4.5mm airgun BB's instead of plastic catches. The mechanism turns freely forward, locks solid backwards, see the video. It has a 1/4" hex in the axle for screwdriver bits. You could also use it as an overrunning clutch.
Name Last modified Size Description
Parent Directory - spragg5-hub.stl 23-Feb-2016 09:21 485K 4-ball Hub Only spragg5.scad 23-Feb-2016 09:21 2.1K Source code, needs util.scad spragg5-fixed.stl 23-Feb-2016 09:21 840K Complete Parts, 4-ball Version spragg5-hub-nospring.stl 23-Feb-2016 09:21 428K spragg6-hub.stl 23-Feb-2016 09:21 668K 6-ball Hub Only spragg6.scad 23-Feb-2016 09:21 2.1K Source code, needs util.scad spragg6.stl 23-Feb-2016 09:21 1.1M Complete Parts, 6-ball Version util.scad 09-Jan-2017 19:28 6.2K images/ 10-Jan-2017 19:04 - Image Pile
It prints in 3 pieces - the axle and two halves of the case. Fit the six BB's into the axle as you slide it into the casing, then glue on the lid.