G - Servicar three wheeler, 1937 to 1972.
E - Overhead valve 61 cubic inch "big twin" (Engine/trans separated).
F - Overhead valve 74,80 or 88 cubic inch "big twin".
FL - 80 to 88 cubic inches and a fat front tire (Also 74" 1941-82).
K - Side valve 45 and 55 cubic inch sports bike that replaced the WL in 1953 and was replaced by the Sportster® in 1957. It had many design features that were carried over to the Sportster®.
U - Side valve 74 or 80 cubic inch "big twin".
V - Side valve 74 cubic inch 1930-36. (Also 1935-36 VLH, VHS 80).
W - Side valve 45 cubic inch made 1937 to 1952.
X - Sports and special construction. Applied to 1918-1922 opposed twin Sport, 1944 military opposed twin, and 1957 to present Sportster®.
The second letter of the model designator reveals the front end (except Sportsters®):
X - Narrow tire and sport forks.
L - Wide front tire and Hydra-Glide front forks.
The third letter of the model designator reveals the frame style:
D - "Dyna®" frame (with the rubber mounted motor).
HT - "Highway Touring" frame.
ST - "Softail®" frame.
The Remaining Characters:
These indicate the model bike within the frame family, or acronyms of the model name.
A - Military (Army) version (except GA, Servicar without tow bar).
B - Battery start (early models), Belt drive (early 80's) Black paint.(1995-6 model, the Bad Boy).
C - Classic, Competition, Custom, various others meanings.
D - Dyna®, the newest frame and engine mount design.
DG - Disc Glide.
E - Electric start.
F - Foot shift (when the standard was hand-shift) and now "Fat Boy®".
H - Varied between High performance, hand shift and Heavy duty.
I - Signifies Fuel Injection.
L - Big fat front tire.
LR - Low Rider (though many Low Riders don't include LR in the model ID).
N - Nostalgia.
P - Police version.
R - Rubber mounted engine (some models) racing version (other models).
ST - Soft Tail.
S - Springer.
S - (without following T) Sports version.
T - Touring.
WG - Wide Glide.
X - Sportster® or Sportster-type front end and narrow front tire.