Abstract: In a multi-pole plug connector assembly including pin and socket housings having contact carrying inserts connected therewith, the fastening screws used to connect the inserts with the respective housings have three different head configurations to serve as coding elements for indicating proper orientation of the housings for plugging connection therebetween. One of the three different head configurations can be combined only with itself while the remaining two head configurations can be combined only with each other. A large number of coding possibilities can be obtained for a plurality of adjacent connector assemblies without increasing the space requirement of the assembly and without decreasing the number of poles or pins being connected.