Connecting system with locking structure

An plug connector, which can mate with an receptacle connector having a locking portion, comprising:

• a second housing which extends forwardly to form an upper mating board and a lower mating board;
• a plurality of second terminals, the each second terminal having a mating portion and a tail, the mating portions of these second terminals being respectively provided at a lower side surface of the upper mating board and an upper side surface of the lower mating board, these second terminals comprising two current terminals and a plurality of differential signal terminals, the mating portions of the two current terminals being provided oppositely up and down respectively at the lower side surface of the upper mating board and the upper side surface of the lower mating board, and width of the mating portions of the two current terminals being greater than width of the mating portions of these differential signal terminals;
• and
• a second cage which is mounted to an outer periphery of the second housing;
• the second cage being shaped as a convexity which is big at a lower side and small at an upper side, and comprising a main body portion and a protruding portion positioned above the main body portion and having a smaller width;
• the main body portion of the second cage and the upper mating board and lower mating board of the second housing being enclosed to form a second mating cavity, the protruding portion of the second cage and the upper mating board of the second housing being enclosed to form a latching cavity;
• the plug connector further comprising a hook, the hook comprising a fixed portion positioned at a rear end thereof and a hook portion positioned at a front end thereof, the hook portion being capable of moving up and down in the latching cavity and protruding upwardly from the protruding portion of the second cage.