How about the Allen wrench
1. It is simple and lightweight.
2. There are six contact surfaces between the hexagon socket screw and the wrench, which are fully stressed and not easily damaged.
3. It can be used to screw the screws in deep holes.
4. The diameter and length of the wrench determine its torsion force.
5. It can be used to screw very small screws.
6. Easy to manufacture and low cost.
7. Both ends of the wrench can be used.