Here is what I copied from someone who ordered axles:
1. TYPE OF REAREND - choose (10 bolt 8.5")
2. BEARING SEAT DIAMETER - choose (1.618")
3. DRIVER SIDE "C" (OVERALL AXLE LENGTH) - fill in (31.8")
3. PASSENGER SIDE "C" (OVERALL AXLE LENGTH) - fill in (31.8")
4. HUB PILOT ("A") fill in (3.060")
5. BOLT CIRCLE - choose (5 X 5" (CHEVY, FORD))
6. STUD TYPE (does not include studs, must order separately) - choose (.505" Knurl Press-In)
7. 2ND BOLT CIRCLE (IF NECESSARY) - choose (none)
8. AXLE FLANGE DIAMETER ("J") - 6 9/16 inch
9. TYPE OF BRAKES/MANUFACTURES PART NUMBER - (drum brakes)
10. TYPE OF DIFFERENTIAL/MANUFACTURE - (auburn limited slip)
-the following fields are optional and I left them blank.
11. AXLE FLANGE TO AXLE FLANGE ("D")
12. HOUSING END TO HOUSING END ("E")
13. DRIVER SIDE HOUSING END TO PINION CENTER ("F") (DO NOT measure through the tubes)