Inner round steel,Outer natural rubber

2.5 / 5 / 7.5 / 10 / 12.5 / 15 / 17.5 / 20 / 22.5 / 25 / 27.5 / 30 / 32.5 / 35 / 37.5 / 40 / 42.5 / 45 / 47.5 / 50

5.5 / 11 / 17 / 22 / 28 / 33 / 39 / 44 / 50 / 55 / 61 / 66 / 72 / 77 / 83 / 88 / 94 / 99 / 105 / 110