This unit replaces the magazine base plate on the SIG P365 (10 round magazines). This extension does not alter the capacity of the magazine. The PG-365 adds approximately 5/8" inch additional gripping surface (1/4" longer than factory extension) as well as enhanced ergonomics. The enhanced gripping surface also incorporates texture which closely matches the frame of the firearm. These units replace the magazine base plate and does not alter the magazine capacity.