This is the FN 309 9mm 20-round extended magazine. 

Maximize your FN 309’s capacity with this factory 20-round extended magazine!

Despite the high capacity, this magazine remains lightweight yet durable thanks to its impact-resistant polymer body. Inside, an anti-tilt polymer follower keeps each round perfectly aligned, delivering reliability when you need it most. 

On top of it all, you’ll find side-facing witness holes that make capacity checks quick and easy. The FN 309 can fill virtually any role, so you might as well stock up on magazines while you can! 

These are sure to sell quickly, so grab a few today!