Mark 4 Remington 700 SA 1-pc 20 MOA 8-40 Adaptable Matte Finishby LeupoldLeupold’s Mark 4 8-40 Adaptable Mount - lso available in a 20-MOA Long-Range Shooter version - is the first mount that can accommodate both the 8-40 screw and a modified 6-48 shoulder screw. Larger through holes accept the thicker 8-40 screw and while the standard 6-48 screw has been replaced by a shoulder screw to work with the larger opening. This gives you the flexibility to mount your rifle with the common 6-48 screw size and or drill and tap your gun to accept the 8-40 screws. These bases will fit Winchester PBR and Remington Super Magnum and HS Precision and and other 8-40 rifles without modification. (Some firearms will not work with these adaptable mounts)Note: MOUNTING LARGE RIFLESCOPES ON LARGE CALIBER FIREARMS WITH CONVENTIONAL 6-48 SCREWS IS NOT IDEAL and AS THE INCREASED RECOIL AND SCOPE WEIGHT CAN OVER-STRESS THE SMALLER SCREWS AND LEAD TO POSSIBLE FAILURES. MORE RUGGED and 8-40 SCREWS INCREASE MOUNT STRENGTH BY 41%.