How to choose the automotive screw finish and hardnessdo you know how to choose the automotive screw finish and hardness?
Selection of surface treatment
a. The principle of color selection of automotive fasteners is to match the clamped parts. In the case of non appearance parts, silver white is preferred;
b. Fasteners can adopt different anti-rust grades according to different parts of the car;
c. When the mechanical performance level is greater than 8.8, galvanizing passivation is not recommended for surface treatment, and non-electrolytic zinc coating is generally recommended. It is not recommended to use galvanized passivation for surface treatment of spring washers and other fasteners with a hardness higher than 350HV to prevent possible hydrogen embrittlement failure.
Selection of level hardness grade
Under normal circumstances, the matching of the mechanical performance level of the nut and the bolt, stud or screw is as follows:
a. Grade 8 nuts can be matched with grade 8.8 bolts, studs or screws;
b. Grade 10 nuts can be matched with bolts, studs or screws of grade 10.9;
c. Grade 12 nuts can be matched with grade 12.9 bolts, studs or screws.
Generally speaking, a nut with a higher performance level can replace a nut with a lower performance level. For example, a grade 10 nut can replace a grade 8 nut to match a grade 8.8 bolt, stud or screw.
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