A.牙型角為60°的三角形螺紋 B.牙型角為30°的三角形螺紋 C.牙型角為60°的梯形螺紋 D.牙型角為30°的梯形螺紋
A.50%~55% B.65%~70% C.70%~75% D.80%~85%