This is a replacement adaptor for use with the PARD NV007S Night Vision clip-on scopes. The 45mm aluminum alloy adaptor will accommodate scopes with an external eyepiece diameter of 38.7-45mm. The 48mm adaptor should be used for scopes with an external eyepiece diameter of 41.7-48mm. Attaching adaptors to all of your existing day scopes allows the interchangeable use of the Night Vision clip-on device across multiple day scopes. Simply remove it from one scope and attach it to another in seconds. Now all of your day scopes can be converted to night vision scope use.