Learning to use the Harley Davidson Parts Numbering System.
If you want genuine Harley Davidson parts for your restoration, then you must learn the Harley-Davidson part numbering system. It’s really pretty simple.
The first five numbers in the part number is the part itself. The numbers after the hyphen is the year it first came out. For example, a 45733-48 is a tube plug oil seal used on the front forks of the FL series bikes from 1948 to present. If this part had a letter following the -48, then it would still be the same part but with an upgrade of some kind. (i.e.; 45733-48A). The same part number, 45733-48B, would be the third incarnation of the part but would still work on 1948 to present FL models. Hypothetically, if the part number were to change from 45733-48A to 45733-95, this would mean it changed so dramatically starting in 1995 that you must use that part from 1995 to present while the dash -48A number would work from 1948-1994 models.
Nuts, bolts, washers, common hardware and most o-rings do not fall into this part number system. They typically have up to five numbers only (i.e.; part number 11105 is a rubber o-ring where as part number 0207 is a washer).
Keeping it accurate is the key you’ll need for using the correct part for the year motorcycle you have.