What are the application standards for screws?

The standards for screws include: product name (standard), material, strength grade, specification and surface treatment.

1. In terms of product type, the torque of hexagonal screws is relatively larger, the torque of hexagonal screws is smaller, and the torque of cross slots is even smaller. In the matching use of products, it is generally recommended to use screws with a grade higher than the nut grade, which is the most economical.

2. Product material grade, here we mainly talk about the carbon steel commonly used for screws. According to the carbon content, it is divided into: C1008 (corresponding to grade 4.8), C1035 (corresponding to grade 8.8), C1045 (corresponding to grade 10.9), SCM435 (corresponding to grade 12.9 and 45H), among which the higher the carbon content, the harder the material. Screws from grade 8.8 to above are all high-strength screws.

3. For specifications, such as M4x8, the outer diameter of the 4-finger thread is 4mm, and the effective length of the 8-finger embedded in the object is 8mm. Generally, the countersunk screw is loaded with the total length, and the semi-countersunk screw is loaded with half the length of the head. The cross of the pan head screw does not include the head size.

4. When the same material is heat treated, the higher the hardness, the worse the toughness. Heat treatment is required for electroplating of grade 8.8 and above. There are two types of heat treatment currently done: high-strength screws require tempering heat treatment, that is, the hardness of the screws is uniform from the inside to the outside; self-tapping screws require carburizing heat treatment, that is, the surface of the screw is infiltrated with a layer of carbon, which is very hard, but the inside is very soft. If carburizing is carried out inside, the screw will be scorched.