The difference is definitely the screw size. In 2021 Savage changed to a larger screw thread size on most of their centerfire rifles, so you either need to identify the production date or take a good look at the screws from the factory base. The size difference will be evident. An in law of mine bought an Axis rifle last year and the shop had a base. Problem was the base was for an older production rifle and the rifle had the larger size threads.