The Pearce Grip Extension 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. These units blend with the contours and fourth generation texture of the handgun giving a factory appearance.*Note- only for magazines equipped with double notches for the ambi magazine release (Gen 4&5 magazines).May need modification when used on some Glock 33's.