a longitudinal insulating housing defining a plurality of grooves;

a plurality of contacts received in the grooves, each contact having a contacting arm, a retaining portion retained into the insulating housing and a soldering portion, the contacts comprising a plurality of signal contacts and grounding contacts, at least two signal contacts defining a signal group and at least one grounding contact defining a grounding group, each signal group and each grounding group being alternately arranged, and a distance between a signal group and a adjacent grounding group being larger than a distance of adjacent signal contacts in a same signal group;

wherein a groove between each signal group and a corresponding adjacent grounding group keeps empty without any contact;

wherein the contacts have a plurality of power contacts, which are arranged on a side of the signal and grounding contacts and have a space from the nearest grounding contact or signal contact;

wherein the insulating housing has a main body, the main body has a peripheral wall, a receiving space surrounded by the peripheral wall and a mating portion extending from center of the receiving space and upwardly extended beyond the peripheral wall, the grooves are formed on opposed side surfaces of the mating portion, and a rib positioned along each side end of the mating portion; and

wherein the slots are formed on inner side surfaces of the peripheral wall and are corresponding to the grooves, the retaining portion is retained in the slot, the contacting arm upwardly extends from the retaining portion to be received in the corresponding groove formed on the mating portion, and the soldering portion horizontally and outwardly extends from the retaining portion.