A.350 B.300 C.250 D.200
A.18m<l≦30m B.24m<l≦60m C.30m<l≦60m D.18m<l≦60m
A.H/500且不應大于20mm B.H/1000且不應大于20mm C.H/500且不應大于25mm D.H/1000且不應大于25mm