When we introduced the MTX 365 for 10-round SIG Sauer magazines, thousands of customers immediately noticed the difference. The improved ergonomics made their 12-round factory magazines feel obsolete. While they loved the upgrade, they were left with costly magazines they no longer wanted to use. To bring new value to these magazines, we created the MTX 365 +3 12-round kit, converting factory 12-round magazines into 15-round magazines. This upgrade makes them perfect for backup or glove box storage. Designed and engineered in house, this kit uses the original magazine housing while replacing key internal components for enhanced performance. It comes with a lifetime warranty and the same rock solid reliability expected from all our products. The SIG P365 Mag Extension is specifically designed for factory 12-round magazines and standard P365 frames. Its custom engineered spring ensures unmatched reliability and guarantees last round bolt hold open. Compatible only with the factory 12-round 9mm magazine and standard sized P365 grip frames Incompatible with X or XL grip modules Comes with the easy loading follower Increase your P365 9mm 12-round magazines to 15-round The Sig P365 9mm magazine extension is proudly made in the USA Designed with an exclusive patented innovation, ensuring 100% dependable functionality The grip extension enhances grip and control significantly, offering superior performance without the need for an XL frame Precision-engineered custom spring