Package details:
M1*10 ----80pcs,
M1.2*16 ----80pcs,
M1.6*25 ---- 60pcs,
M2*30 ---- 40pcs,
M2.5*30 ----40pcs,
M3.2*40 ---- 20pcs,
M4*60 ---- 20pcs

Also called a spring pin, used for thread locking. After the nut is tightened, insert the cotter pin into the nut slot and the tail hole of the bolt, and open the cotter pin tail to prevent relative rotation between the nut and the bolt.