3 x lacquered brass rings with glass inserts.The outer diameters are 40mm and the glass middles have a diameter of 27mm. The brass rings are seperately stamped, '3ft, 6ft, 9ft'. The glass middles are held in place with a sprung brass collar. They all have a thread at the back with a diameter of 31mm. The rings sit comfortably on the black metal holder, which may be irrelevant if the rings are threaded.Maybe unassociated with microscopy but they were included in a box of microscope part...s.