screw member 7 lockable to a panel not shown the insulative housing 2 approximately in the shape of a cubical block defines a front face 201 and a pair of side surfaces perpendicular to the front face 201 the housing 2 is formed with a first housing 21 defining a center receiving cavity 210 and a cylindrical second housing 22 protruding into the receiving cavity 210 of the first housing 21 the second housing 22 has a front face not labeled flush with the front face 201 and defines a fine receiving groove 220 along a longitudinal axis thereof a round rim 211 is formed on the front face 201 of the insulative housing 2 along a front fringe of the receiving cavity 210 the housing 2 comprises a first section 212 a second section 213 and a third section 214 which are arranged in turn along a vertical direction of the housing 2 the first section 212 defines a pair of foursquare recesses 2120 at opposite ends thereof a first rectangular passage 2121 in the center of the first section 212 along a rear to front direction a pair of first channels 2122 recessed laterally from opposite inner surfaces of the first passage 2121 and a pair of first latching openings 2123 in communication with the first channels 2122 and located in a middle of the first section 212 a pair of slits 2124 is defined near bottom surfaces of the corresponding recesses 2120 the second section 213 defines a.