Abstract: A system is provided for mechanically keying a number of cable connectors using a binary coding system to assure within a given set of cables that only one, unique matching set is defined. Binary keying is provided using 2×n holes aligned on each face of opposing key mounting surfaces, the holes aligned such that when a post is secured in a hole on one of such mounting surfaces, it will be received by a matching hole in the opposing mounting surface, provided said opposing mounting surface has been complimentarily keyed. The holes are arranged as bit pairs whereby each hole of the bit pair is assigned as the “0” and “1” position, the bit designated as either “0” or “1” depending into which of the paired holes a keying post is placed. By this system up to 2n uniquely keyed combinations can be provided.