Harley model designations are a sequence of letters and numbers, combined in limited ways. The sequences can be long, as in the 2006 model designation FLHTCUSE.
The first letter may be one of the following:
E, J, K ('50s small twin), F, U, V (Big Twin), D, G, R, W (Small Twin), X (Sportster), or V (VRSC)
Letters are appended singly or in pairs, as follows:
B (Belt Drive), C (Classic or Custom), D (Dyna Glide), DG (Disk Glide), E (Electric start), F (Fat Boy (1990-present) or Foot-shift (1972 and prior)), H (High compression), L (Hydra Glide forks), LR (Low Rider), P (Police), R (Race or Rubber-mount), S (Sport, Springer, or Standard), SB (Single belt final drive), ST (Softail), T (Touring), WG (Wide Glide), I (Fuel injection), SE (Screamin’ Eagle), U (Ultra)
Custom Vehicle Operations models can also have a number (2,3,4) added.
Note that these conventions for model designations are broken regularly by the company.