|There were different numbers for early K-models, but by the time 1954 rolled around, the third year of the K-model, this gear has stayed the same.
I am pretty sure it will retrofit to earlier years. Note the BOM table in the countershaft sub-assembly page.
Thing is, the -52 part has 26 teeth, the -54 has 24, and the -54A has 23 teeth. So you have to retrofit the mate as well.
This page will be updated later with what to look for as this part wears or fails.
The left countershaft has a spiral gear as part of the low or 1st gear.
It drives the speedometer on 1952 to 1972 models. The right countershaft
is what would be used on 1973 to 1984 Iron Sportsters, the speedo is
from the front wheel.
3nd gear is in between 1st , or "low" gear and 2nd gear. It is not
the third gear on the shaft but the gear that is transmitting power
when you are in third gear.