Shrewd Optum Ring System 40mm/35mm .015 Pin Black. With multiple rings it is possible to change between the two just by removing two screws and pulling the ORS from the scope body. Must be purchased for use with Optum Scope. Specifications for Shrewd Optum Ring System: Manufacturer: Shrewd Color: Black Package Contents: Shrewd Optum Ring System Shrewd SMSORS015: Optum Ring System 40mm/35mm .015 Pin Black