发明授权
US5772376A Countersunk head screw 失效
沉头螺丝

Countersunk head screw
摘要:
The invention relates to a countersunk head screw with an even number of ribs with countersinking blades on the underside of the screw head and projecting therefrom. Every other rib has a step at its end towards the screw shaft formed by shortening the rib concerned in relation to each adjacent rib.
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