The TTI 4mm baseplate extension is designed specifically for 2011 style magazines in 9mm/.38 caliber providing a +2 round capacity increase while maintaining USPSA compliance.TTI 2011 Magazine Baseplate Extension - 4mm Profile+2 Round Capacity (20 to 22 rounds with factory spring and follower)Compatible with Staccato/Infinity/Springfield Prodigy/Atlas/Infinity magazinesRecommended for 140mm magazinesFits USPSA 140mm gauge requirementsBlack finish with hard coat anodized constructionIdeal for competitive shooters and tactical applications this mid-profile extension works with all 2011 style magazines while being optimized for 140mm configurations ensuring reliable function with factory components.