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1 以1/4-20UNC之螺絲攻進行攻牙時,其攻螺紋鑽頭(tap drill)的直徑約為多少mm? 100 統測
A 4
B 5
C 6
D 7

攻螺絲之前的鑽孔直徑 = 螺紋外徑-節距

= 14” - 120

= 5-120

= 15

= 25.45

≒ 5mm