This magazine is compatible with your FN 509. It is constructed of stainless steel with at flat black finish, high visible anti-tilt follower, and flat base pad.*Note- This mag will not work with FNS TM or FNX TM pistols.
Specifications:

Caliber	9mm Luger
Capacity	17
Finish	Black
Model	509
Material	Stainless Steel
Type	Detachable
Model Fit	FN 509
Brand Fit	FN
Max Capacity	17