These units replace the magazine base plate and internal floor plate. They will add two rounds to the Glock M26, one round to the Glock M27 and M33 and no rounds to the Glock M39. These units will add 5/8" additional length for better control and comfort. ***Fourth Generation Magazines ONLY These units blend with the contours and fourth generation texture of the handgun giving a factory appearance. They are made from High Impact Polymer and withstand drop tests at temperatures from -20 F to 350 F. They form the next logical finger positioning feature to provide control and comfort without sacrificing conceal ability.