It depends on the model and options. For example, in 2003, the base drums are 9". Adding any one or more of these options got you the 10" upgrade:

4x4
Edge
Supercab
Payload Package #2

Later years similar.

Basically, the 9" are only for 2WD regular cab XL / XLT with base payload. Since yours is a 4x4 S/C, it definitely has 10" drums.


As stated above, the 9" are finned on the outside, 10" are smooth.

__________________
2003 FX4 Level II, Supercharged 5.0L V8, Headers, Duals
BW4406 manual transfer case, Aussie Locker, Torsen L/S, 4.10's
Bilstein 7100 rezzies, Cadillac/Mustang rear discs, Duff traction bars
Keypad Entry, Lock LEDs, ABS switch, sway bar discos
Heated seats, Explorer EATC, Trip Computer and consoles

2003 XLT 2.3L M5OD-R1 reg cab, 2011 Taurus SEL, 2016 C-MAX Energi Plug-in Hybrid