An assembly includes a receptacle and a plug. The plug comprises a plug insulative housing with a front mating region, a plurality of plug contacts disposed in the housing with plug contacting sections exposed upon the mating region and a plug metallic shell enclosing the front mating region to commonly define a plug mating port. The plug metallic shell defines essentially a rectangular cross-section including two opposite long sides and two opposite short sides perpendicular to each other. A pair of chamfered structures is formed on two opposite corners along one of the two long sides, and a centered recessed area is formed on the other of said two long sides. The front mating region intimately abuts against the other of the two long sides. The receptacle has a receptacle metallic shell with a similar contour of the plug metallic shell.