L indicates a left-handed screw, and a right-handed screw is generally not marked.
Level 7 screw, used for feed motion of transmission, screw lathe, external grinder, surface grinder, etc.
8-level lead screw, general drive, general lathe and thread milling machine.
Grade 9 screw is used for low-precision transmission, such as indexed feed screw.
Accuracy grade, pitch tolerance, cumulative pitch tolerance in the following length (mm), cumulative pitch tolerance in the following thread length (mm).