A.1/3 B.1/4 C.1/2
A.α≤30° B.α≤45° C.α≤60°
A.開孔最大直徑d≤1/4Di,且d≤800mm B.開孔最大直徑d≤1/3Di,且d≤1000mm C.開孔最大直徑d≤1/2Di,且d≤1200mm D.開孔最大直徑d≤1/5Di,且d≤520mm