FF: Full floater, the one with the big hub with two bearings that sticks through the wheel center.

SF: Semi-floater, with an axle flange the wheel bolts onto and a single bearing pressed onto the axle or in the housing. Semi-floaters usually have 5 or 6 lug studs, full floaters have 8 or more. The full-float axle shafts can be removed while the wheels and hubs stay on the vehicle.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!