This extension replaces the magazine floor plate adding two rounds capacity to Glock factory 20,21,29,40 and 41 magazines. This unit is for use on high capacity magazines only, it will not work on the 10 round M20 and M21 magazines. Not for use on Glock M30 10 round magazines.FeaturesHigh Impact Polymer MaterialWithstands Temperatures from -20 F to 350 FAdds Two RoundsNote250 round break in period required on many of the newer magazine springs to allow for easier loading of the last extra round.These units will work on both third and fourth generation Glock modelsThese units will work on Glock M30 9 round magazines, enabling the magazine to hold 11 rounds. DISCLAIMER: This product is not manufactured, authorized, endorsed, or warranted by GLOCK. GLOCK does not warrant or represent that this product is compatible with GLOCK pistols.