Keying system for electrical connectors

A keying system for a plurality of electrical connectors having different numbers of terminals, comprising:

• a plurality of male connectors each having an elongate housing with a plurality of silos projecting from the housing in only two parallel rows longitudinally of the housing, the silos of first and second rows of said parallel rows, each having generally rectangular cross-sections defining opposite first and second sides running longitudinally along the housing, the first sides of the silos of each row being in a common line generally parallel to said rows, and a plurality of terminals mounted within the housing of said male connectors with contact portions of the terminals projecting into the silos;
• a plurality of female connectors each having an elongate housing with a plurality of receptacles in only two rows for mating with the silos of the male connectors, the receptacles of first and second rows having generally rectangular cross-sections defining opposite first and second sides running longitudinally along the housing, the first sides of the receptacles of each row being in a common line generally parallel to said rows, and a plurality of terminals mounted in the housing of said female connectors with contact portions located in the receptacles for mating with the terminals of the male connectors;
• said mating male and female connectors being provided in sets of connectors with a male and female connector in each set, there being at least four sets of said mating connectors, each set of said connectors being adapted for mounting at least two pairs of mating terminals, with number of mating terminals in any given set of connectors being different from the number of any other set of connectors, and the number of mating terminals in the at least four sets of mating connectors increasing in a predetermined progression such that the connectors have increasing lengths as a function of the number of mating terminals on the respective connectors;
• and
• at least some of said silos of the male connectors and said receptacles of the female connectors including flattened corners only on said second sides thereof such that either connector in any given said set of connectors cannot mate with a connector of any other set thereof.