Reptilia Blackhole, Magwell, Black For Glock Gen 3 & 4 19/23 100-005 Introducing the Reptilia Black Hole(TM) Polymer Magwell for GLOCK(R) pistols. Molded from reinforced polymer" the Black Hole's enlarged magazine well opening helps facilitate more efficient reloads without adding unnecessary bulk to your carry or duty sidearm. Compatible with 9mm & .40-caliber GLOCK pistols" the Black Hole utilizes a unique rear spacer to ensure seamless fit and compatibility with both Gen 3 & Gen 4 frames. Note: Not compatible with 10 round factory Glock magazines but is compatible with Magpul(R) 10 round magazines.