| 摘要 |
A screw having in its head a recess that includes two or three non-circular superimposed recess-tiers. The depth of each recess-tier is less than 1.35 mm and there is less than 1° draw in each recess. The screw head recess is formed using a punch ( 10 ) in a cold heading process. The punch is formed in a profilating CNC machine, cutting the profiles of the punch to a tolerance of better than ±0.0025 mm.
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