a rejection apparatus adapted for selective installation in a female electrical socket to prevent mating of an incompatible male connector . the apparatus is formed of an elongated body of dielectric material and includes a segmented spherical head portion adjacent one end . the spherical head portion is designed to resiliently compress to allow insertion into a connector sleeve of the female socket . the head portion snaps outwardly into retaining engagement at an inner end or shoulder area in the sleeve . the spherical head portion also includes a shoulder which can engage an associated inner portion of the female socket to limit axial movement of the apparatus . when in position in the sleeve , the opposite end of the apparatus extends outward to function as a rejection element . the end is color coded to give a ready visual indication of the presence of a rejection apparatus in the sleeve . also disclosed is an installation tool arranged to resiliently grasp the rejection apparatus for insertion into the connector sleeve .