1) 2 rings 2) Ring shape: R(O), D, Q, A; 3) With /without booster; 4) ... 2 rings, 3 rings, 4 rings...2) Ring shape: R(O), D, Q, A; 3) With or without booster;4) ... buffer space, avoids deformation, bending during transportation and production process, which reduces damager rate===================================================================================================Established in 2000, Hui Feng ...