A.D/2 B.d/2 C.(D-D1)/2 D.(D+D1)/2
A.0.015~0.03 B.0.004~0.07 C.0.07~0.075 D.0.03~0.04
A.兩端硬,中間軟 B.兩端軟,中間硬 C.一樣硬 D.一樣軟