This magazine is compatible with your FN FNS/FNX. It features a darkened steel with low-friction follower and polymer base pad.
Specifications:

Caliber	40 S&W
Capacity	14
Finish	Steel
Model	FNS-40/FNX-40
Material	Steel
Type	Detachable
Model Fit	FNX-40
Brand Fit	FN
Max Capacity	14