These weights are compatible with AI AT-X Rifles, and allows the shooter to balance their rifle on their bag. They can be installed close to the action or close to the end of the rail, and the user can stack two of either size together. The user can also mix AXSR weights and AT-0X weights together based on preferences. Fasteners sold separately. Accuracy International AT-X Keyslot Steel Side Weights 6/pk 009-1003KIT