It will fit in the airbox a little loose, but when you attach it to the mount it should snug up. If you can hear it rattling around or something after its all put together you probably have the wrong filter.
1996 F150 Single Cab 4x4 Inline 6-SOLD
2002 F150 SuperCrew Lariat FX4 5.4-SOLD
2012 F150 SuperCrew XTL 4X4 5.0
1999 Mustang Cobra