High-strength aluminum alloy 1913 Picatinny base attaches to the receiver with 8 screws. Compatible with both Weaver and Picatinny rings. Only fits long action X-Bolt rifles. - Getting more out of the phenomenal accuracy of the X-Bolt. Reports from shoots all across the world confirm that today's X-Bolt rifle is an incredible shooter capable of incredible accuracy. For those of you looking to reach out a little bit further this high-quality base provides you a solid lock-up to your action and an additional 20 MOA of elevation so you can dial in that much more drop on your scope before you have to start stacking MOA/Mils.