anyone know what the axle codes are??

 

I don't know them, you could probably search for them. Your axle is 3.55 if you have an STX

 

Here you go:

19 — 3.55 non-limited slip — F-150
25 — 4.10 non-limited slip — F-150
26 — 3.73 non-limited slip — F-150/Mark LT
27 — 3.31 non-limited slip — F-150
B5 — 4.10 limited slip — F-150
B6 — 3.73 limited slip — F-150/Mark LT
H9 — 3.55 limited slip — F-150

 

Thanks PHS79. Mine was H9