The common Deere part number is in the form:
Letter - identifying the machine and/or model
Number - 1 to 6 digits identifying the part
Letter - identifying the originating factory
If the part is an assembly of multiple pieces it will be prefixed by the letter A for Assembly.
A - Model A tractor and its successors 60, 620, 630
B - Model B tractor and its successors 50, 520, 530
C - Model GP tractor
D - Model D tractor
E - Model E stationary engine
F - Model G tractor and its successors 70, 720, 730
H - Model H tractor
L - Model L tractor
M - Model M tractor and its successors 40, 320, 330, 420, 430, 435, 440
R - Model R tractor and its successors 80, 820, 830, 840, and most New Generation and later Waterloo tractors
T - Most New Generation and later Dubuque tractors
Notable exceptions above are:
C for the GP line: the GP originally came out as the model C (smaller version of the existing D)
F for the G series: the G was originally slated to be called the model F.
Implement prefixes
Z - Mowers
P/H - Combines
Factory codes
A = John Deere Plow Works, Moline, IL
B = John Deere Planter Works, Moline, IL
C = John Deere Spreader Works, East Moline, IL
D = John Deere Wagon Works, Moline, IL
E = John Deere Ottumwa Works, Ottumwa, IA
F = Syracuse Chilled Plow Company, Syracuse, NY
H = John Deere Harvester Works, East Moline, IL
K = John Deere Killefer Works, Los Angeles, CA
M = John Deere Horicon Works or John Deere Van Brunt Company, Horicon, WI
N = John Deere Des Moines Works, Des Moines, IA
R = John Deere Waterloo Tractor Works, Waterloo, IA
T = John Deere Dubuque Tractor Works, Dubuque, IA
U = John Deere Industrial Equipment Works
W = John Deere Welland Works, Welland, Ontario, Canada
Y = John Deere Yakima Works, Yakima, WA
X = All Factories above mentioned
Z = Zweibrucken, Germany