Since each firearm manufacturer has their own proprietary mounting rail design, each ring model must be machined to exacting tolerances for proper fit and function. Because of this, the Warne Ruger Rings are able to fit right onto the receivers dovetail with no need for a mounting base.Lastly, The Ruger Fixed Rings utilize 4 T-15 Torx style socket cap screws for secure and permanent optics mounting.