They print strongest with ~50% fill, printed vertically, thick side up. It only works for fairly low torque, but can be helpful to start a screw in a screw in a hard-to-reach place if it is possible to finish with a proper driver. I get decent performance when using the bit at angles under 20 or 30 degrees. It's based on a modified version of someone else's universal joint, but in the future I'd like to find a stronger joint for higher torque.

Will require some sanding to get everything together. Mine has pretty tight tolerances.