I'm wondering what the most efficient way to transfer torque is. I'm not talking about which shape can handle the most torque but rather how can I transfer 100% of the torque. Lets take screw bits for example. It seems to me that the simple slotted or philips head transfer 100% of the torque because the force of rotation generated by the torque is applied completely perpendicular to the surface and hence all the force (and torque) is transfered. Compare this to for example an allen or a torx where the force is not perpendicular and hence some force gets waisted. Is this correct? If yes I have the following issue. I have the following two metal surfaces sticking out as in the images attached which I am trying to rotate (with e.g. a screwdriver). In the circular one, the torque (generated by the screwdriver) generates the largest force in the F1 direction. However, that's not possible given the shape of it so it can only apply force in the F2 direction, which is the projection of F1 onto the perpendicular direction of the flat surface. On the flat surface sticking out, the torque generates maximum force perpendicular to the surface and hence this would transfer 100% of the torque. (the exact same wound he true for any flat surfaces. such as a philips.) Am I correct here? Thank you very much for your time!