The screw is inclined. The screw is an inclined plane twisted into a cylinder, and the length of the thread grain and a circle of thread on the screw is equivalent to the length of the inclined plane. An object with inclination can be regarded as an inclined plane, this can be regarded as a slide, and the slide is an inclined plane. Bevel is a simple machine. Screw is a kind of nail that uses the principle of inclined plane to drill into solid material in a spiral way. Screw is a tool to tighten instruments and parts step by step by using the physical and mathematical principles of circular rotation and friction of the inclined plane of an object.

Classification of inclined planes:

1. Convex slope. A steep slope is called a convex slope, and some sections cannot be seen through. On the map, from the top of the mountain to the bottom of the mountain, the interval is a group of contour lines with sparse upper surface and dense lower surface, which is characterized by convex slope.

2. concave slope. Slopes with steep slopes and gentle slopes are called concave slopes, and all slopes can be seen through. On the map, from the top of the mountain to the bottom of the mountain, the interval is a group of contour lines with dense upper surface and sparse lower surface, which is characterized by concave inclined surface.

3. wavy slopes. In the field, there are irregular inclined planes with cross transformation, different steepness and fluctuation, which are called wavy inclined planes, and some sections cannot be seen through. On the map, the contour lines representing this slope are unevenly spaced and irregular.