Olympus CH-2 microscope Phase Contrast-1 annuli without mount. The product  number is B-L0126 and is new not in original packing. The 2004 Olympus catalog describes as centerable Pop- 10X annulus for CH2-CD with a list price of $82.00.  It measures 15.8 mm X 1.2 mm. and is intended to be used in the substage condenser.  As far as I know, it will only fit the CH-2 and will not guarantee any other application  Thanks for Looking!