Screws refer to parts used in construction machinery. It is a type of threaded parts with sharp ends such as nails, small cylindrical or conical metal rods, and heads with grooves or dimples, which are used alone. 1. Screws can be divided into Machine screws, self-tapping screws, drill-tail screws, wallboard screws, fiberboard screws, wood screws, hexagonal wood screws, captive screws, combination screws, micro screws, furniture screws, electronic screws Second, according to the head shape can be divided into 1. Hexagon head 2. Hexagon head with flange 3. Square head 4. T head 5. Mushroom head (truss head ) 6. Cheese head 7. Round head 8. Pan head 9. Countersunk head (flat head) 10. Raised countersunk head Three, according to the groove can be divided into 1. Philip 2. Ten/One word 3. One word 4. Inner triangle 5. Inner corner square 6. Cross 7. Rice word 8. Flower shape 9. Plum blossom shape 10. Flower shape one word 11. Special shape 12. Inner hexagon