Pearce Grip PG1045+ Magazine Extension for Glock 20/21/29/40/41 Black Finish This extension replaces the magazine floor plate adding two rounds capacity to for Glock factory M20 45ACP and M21 10mm magazines. This unit is for use on high capacity M20 and M21 magazines only, it will not work on the 10 round magazines. Finish: Black Material: Polymer Type: Magazine Extension Model Fit: G20/21/29/40/41 Brand Fit: for Glock