These are our most popular matrix of Standard Series diaphragms offered in aluminum mounts. The tolerances are held tightly to ensure perfect centering of the diaphragm within the mount. Mounting holes are centered to offer easy integration into optical breadboard configurations. For the ½" maximum aperture (smallest), a 8-32 to ¼-20 thread adapter is available (#53-926). For additional information on the Mounted Standard Series Iris Diaphragms, match the aperture range with the standard series table.