A plug for mating with a receptacle includes: an insulator that has an inner bottom surface, which is orthogonal to a mating direction of the plug; and a plurality of pin contacts secured to the insulator and aligned in an alignment direction, each of which includes a contact tab having a pair of planar surfaces of the contact tab on two mutually opposite sides thereof which are parallel to each other, the planar surface of the contact tab each forming a contact surface. The contact tabs stand up from the inner bottom surface in the mating direction, the contact surfaces being parallel to the alignment direction. A plurality of protrusions are formed in the insulator that stand up from the inner bottom surface in the mating direction, such that each of the protrusions is positioned between two of the contact tabs which are next to each other in the alignment direction.