The two rows of the plurality of the terminal grooves 124 include an upper row of the terminal grooves 124, and a lower row of the terminal grooves 124 located under the upper row of the terminal grooves 124. The upper row of the terminal grooves 124 penetrate through the upper portion of the rear surface of the limiting portion 121 and the upper portion of the first docking portion 122 along the longitudinal direction, and penetrate through the top surface of the second docking portion 123 along the vertical direction. The lower row of the terminal grooves 124 penetrate through the lower portion of the rear surface of the limiting portion 121 and the lower portion of the first docking portion 122 along the longitudinal direction, and penetrate through the bottom surface of the second docking portion 123 along the vertical direction. Front ends of the upper row of the terminal grooves 124 penetrate through the top surface of the second docking portion 123 and are arranged transversely. Front ends of the lower row of the terminal grooves 124 penetrate through the bottom surface of the second docking portion 123 and are arranged transversely. Two opposite sides of the front surface of the limiting portion 121 protrude frontward to form two limiting ribs 125. Rear ends of the two limiting ribs 125 are connected with two opposite side surfaces of the first docking portion 122, respectively. Front ends of the two limiting ribs 125 are connected with two opposite side surfaces of the second docking portion 123, respectively.