There are 5 different H2 axles and 3 different styles the easiest way to tell is
the end opposite the thread :
1971 - 1972 H2 completely round
1972 Round with a hole 283mm
1973 Round with a hole and 2 flats and 4 mm longer (?)
1974 Large round with no hole and 2 flats and 6mm Longer
1975 Large round with a hole and 2 flats 8mm longer and also uses a washer behind the castle nut.
KH (top) vs Late H1 Front Axle