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 CZ Rings are able to fit right onto the receiver�s dovetail with no need for a mounting base. - The CZ Fixed Rings are available in two different styles to fit either the CZ 550 receiver design (19mm dovetail) or to fit CZ 527 (16mm dovetail) model and utilize 4 T-15 Torx style socket cap screws for secure and permanent optics mounting. - Permanently attaches to base. - CZ specific recoil pin for positive engagement of ring to receiver dovetail. - Rings securely mount around scope using 4 Torx style T-15 socket cap screws 25 in/lb. of torque recommended.