Monstrum Tactical 1" Diameter Scope Ring Inserts for 30mm Scope Rings 1" diameter scope ring inserts fit on the inside of 30mm scope rings, allowing for perfect fit mounting of 1" scope tubes with 30mm scope rings High quality, aerospace aluminum construction, both durable and lightweight The inserts are available in widths of .635 inch (or 16.15mm) or 1 inch (25.4mm). Please note the inserts have flared edges and will not work with scope rings wider than this.