Converter Rings are sold in singles; for Jerry-31 and RNV-31, buy two. The Cold Harbour Jerry Converter Rings allow users to install popular PVS-14 lens accessories onto the following devices: Infiray Jerry-14 Infiray Jerry-31 Infiray Jerry-FB RIX Tactical RNV-31 RIX Tactical RNV-14  Installation is simple: Use the optional (HIGHLY RECOMMENDED) retaining ring tool to remove the factory lens cell retaining ring and screw in the Converter Ring. Install your desired lens accessory such as our NV Defender protective sacrificial lenses or CHAD iris devices.  The Converter Ring is knurled along its circumference, making not only attachment onto the host device easy and secure, but users can separate the ring from any lens accessory easily.  Converter Ring tool made in Canada by Volk CNC Machine NOTE: Cold Harbour is not responsible for damage to the host objective lens from users attempting to remove the retaining ring with or without our tool. Care should be exercised around sensitive optics. The adapter rings will impede with the installation of COTI devices on the Jerry series NVGs.