A plug connector includes an insulative housing with mating slot, contacts disposed in the housing by two sides of the mating slot, and a pair of side arms located by two opposite ends of the mating slot in a horizontal transverse direction. a receptacle connector includes an insulative housing defining a horizontal mating tongue; contacts disposed in the housing with contacting sections exposed upon two opposite surfaces of the mating tongue; and a monolithic horizontal metallic shielding plate disposed and extending substantially fully the mating tongue. The shielding plate defines side protruding edge sections exposed outside of corresponding side edges of the mating tongue and a notch structure on each side protruding edge section, the pair of side arms each defines a hook structure to engagement with the notch structure.