Abstract: Apparatus having special utility for the electrical interfacing of multi-terminal circuit testing equipment to multi-contact printed circuit boards or the like employs a fluid pressure responsive, resiliently flexible diaphragm for controllably effecting concurrent, individual, substantially equal force engagements between shiftable, rigid contacting elements and corresponding stationary contact points on the unit to be tested, despite possible lack of precise co-planarity of such contact points. The arrangement is space conserving and permits the elimination of expensive and troublesome spring contact pins, the utilization of desirable wirewrap connection techniques in fabricating interfacing assemblies, and the convenient disposition of all points of electrical contact with both the testing equipment and the unit under test at one side of the interfacing assembly.