Specifically, a front of the receiving chamber 46 is located between the two side boards 42. The second receiving chamber 413 of the receiving chamber 46 is located between the two side boards 42. A third receiving chamber 421 is surrounded among the two side boards 42 and the at least one sealing board 43, and communicated with the first receiving chamber 411. The two sealing boards 43 are connected with upper portions and lower portions of the rear ends of the two side boards 42 connecting with the base body 41, so that the third receiving chamber 421 is surrounded among the two side boards 42 and the two sealing boards 43, and communicated with the first receiving chamber 411. The shielding element 40 further has a connecting board 44 connected between front ends of the two side boards 42. An opening 45 is formed between the front ends of the two side boards 42 projecting beyond front surfaces of the two sealing boards 43. Middles of two facing surfaces of the two side boards 42 are recessed oppositely to form two limiting slots 422 extending longitudinally. The two limiting slots 422 are corresponding to the two limiting ribs 125, respectively. Middles of a top and a bottom of the base body 41 open two buckling grooves 412 communicated with the first receiving chamber 411.