Commonly used screw specifications include: metric screws, American screws, and imperial screws.

The main categories include ordinary screws, machine screws, self-tapping screws and expansion screws.

The outer edge of the screw head of the hexagon socket screw is round and the middle is a concave hexagon. The hexagonal screw is the common screw head with a hexagonal edge. The hexagon socket screwdriver looks like a "7". It is made by cutting both ends of the hexagonal steel bar and then bending it at 90 degrees to become a hexagon socket screw wrench.

Extended information:

Common types of screws

1. Slotted: one word (Minus).

2. Phillips: Cross (Plus).

3. Phil-Slot: one word/cross.

4. Hex Socket: Internal hexagon.

5. One Way: One-way (can only be locked in, not exited).

6. Flat: Flat head (after being locked in, the top will be flush with the workpiece).

7. Oval: salad head, O head, semi-sunk head.