All 7 9/16" axles (aka Model 15) have the axle ratio stamped on the right axle tube housing boss adjacent to the dowel hole.

Code Ratio Gears
E 3.58 12/43
F 3.08 13/40
G 3.31 13/43
H 2.73 15/41

The 8 7/8" axles (aka Model 20) will have the Axle Ratio Code stamped on the differential housing cover flange.

Code Ratio Gears
A 3.54 11/39
B 3.15 13/41
C 2.87 15/43
D 3.91 11/43

Range of gears for the Model 15 (7-9/16" ring gear): 2.35 (20/47 -- Will someone with a 1982 or 83 TSM check this? That's the only way I could get it to work out even close!) 2.37 (19/45 -- fleet option only) Code J (Twin Grip not available) 2.53 (17/43) Code K (V w/Twin Grip) 2.73 (15/41) Code H (U w/Twin Grip) 3.08 (13/40) Code F (T w/Twin Grip) 3.31 (13/43) Code G (S w/Twin Grip) 3.54 (11/39) Code A (N w/Twin Grip)(EE, FF w/Twin Grip also used, I believe Eagle only) 3.58 (12/43) Code E (R w/Twin Grip) 3.78 (9/34) Pre 1971 (mainly used w/OD or big car, small engine w/auto) 4.10 (9/37) Pre 1971 (used w/OD only) The 2.73 and lower numerical gears use a different carrier than the others due to the size (diameter) of the pinion gear (anything over 13 teeth). Model 20 (8-7/8" ring gear) gear range: 2.56 (16/41) Code X (Y w/Twin Grip) 2.87 (15/43) Code C (O w/Twin Grip) 3.15 (13/41) Code B (P w/Twin Grip) 3.54 (11/39) Code A (N w/Twin Grip) 3.91 (11/42) Code D (Q w/Twin Grip) The 2.56 and lower (numerically) uses a different carrier than the others (more than 15 teeth for Model 20). Lower gears (4.11, 5.00) were offered in the Model 20 as dealer installed options 68-74 or so, but weren't factory installed.