Abstract: A retainer member for inhibiting or preventing relative rotation between a plurality of fastener elements which are arranged in predetermined spaced relationship with each other, and more particularly, an apertured retainer plate for preventing the rotation of nuts which are screw-fitted onto the threaded shanks of bolts so as to facilitate the tightening and torquing or disassembling of the bolts on the nuts. Also disclosed is a plurality of the plate-shaped retainer members being arrangeable in a contiguous relationship with each other and thereby collectively defining a specified bolt circle having the apertures therein located at annular positions in conformance with bolt holes formed in structures, such as mating flanges.