If you have the Glock G17 / G22 magazine, and you want to use it with your Glock G26 / G27 pistol, then this is the right sleeve to fill the gap. Will fit Glock G26 pistol with Glock G17 - 17 / 17+2 magazine.
MagEx2 Extension Kit for Glock Magazine
Glock 22 Grip for sale
DRYFIREMAG™ for Single Stack 43X/48 Glocks
Magazines Archives - Whittaker Country
Glock 27 Gen 5 Magazine FOR SALE! - PicClick
Conversion Kits For Glock: Advantage Arms Secure Online Store
X-Grip Magazine Spacer GL26-27 Other - Arnzen Arms
Universal Double Magazine Pouch, Magazine Holder Fits
X-Grip Glock 26/27 +7 Magazine Spacer, Black - GL26-27
Pachmayr Mag Sleeve Mag Adapter Glock 17, 22 Mags to fit Glock 26, 27
A&G Glock Magazine Spacer Sleeve 21 to 30 Gl29-30 for sale online
Magazine Sleeve/Spacer/Adapter Glock G26/G27 With Glock G19/G23