The Axle arrangement, including wheelset assembly, wheelset or axle assembly, the individual series is an important feature of distinction. When naming the wheel alignment, the number and arrangement of the driven axles and the axles is given. Furthermore, whether axles or axle groups are stored in the main frame or separately from it. The wheel alignment is displayed in a short form alphanumeric. The wheel alignment as we know it today, first developed in 1908 as a system defined by the Association of German Railways. The International Union of Railways (UIC) has defined this in the UIC Code 612, as of 01 January 1983 in the UIC Code 650.

Examples:

1 = a running axle mounted in the main frame
1′ = a running axis independent of the main frame
2 = two consecutive running axles mounted in the main frame
2′ = two consecutive and united in a bogie, but independent of the main frame barrel axles
A = a driven axle in the main frame
B = two driven, coupled, axles in the main frame
A’ = a drive axis independent of the main frame
B’ = two independent of the main frame, coupled together and combined in a bogie, drive axles
Bo1 = two axles in the same frame but individually driven

In the latter case, “Bo1“, the letter is given a small zero placed on the line without a space.

Additional designations in the Axle arrangement for steam locomotives

The following information is added to the wheel alignment, usually at a small distance on the same line.

a) the type of steam

h = superheated steam
n = wet steam
t = dry steam

b) The number of cylinders

2 = two cylinders
3 = three cylinders
4 = four cylinders

c) the type of steam expansion

not specified = single-stage steam expansion
v = composite effect

Additional designations in the Axle arrangement for powered vehicles with internal combustion engine

a) Type of fuel

d = diesel
b = benzene

b) Type of power transmission

m = mechanical
e = electric
h = hydraulic

Additional designations in the Axle arrangement for powered vehicles (electric)

a) the type of electricity

g = DC
w = alternating current
d = three-phase current

b) Type of drive

k = Crank drive without countershaft
u = Crank drive with countershaft (translated)
e = single-axle drive with motors mounted in the frame
t = Tatzlagerantrieb
gf = single-axle drive with bogie-mounted motors with sprung drive

Example of a wheel alignment in a class 181 steam locomotive

2’C 1′ h4v = (2′) Two axles united in one bogie, (C) three coupled axles mounted in the main frame, (1′) with a rear, separate from the main frame barrel axis.
The steam locomotive is a superheated four-cylinder compound express train locomotive (h4v).

Example of a wheel arrangement in a diesel locomotive

Bo’Bo’1-de = (Bo’Bo’) two individually driven axles in two different frame bogies, the fuel is diesel (d) and the Kaftübertragung electric (e).

Example of a wheel alignment in an electric locomotive

Bo’Bo’1-w4gf = (Bo’Bo’) each two individually driven axles in two different frame bogie, the current type is alternating current (w), single-axle drive with motors mounted in the bogie (4 traction motors) with sprung drive (gf).

1Bo – the o should represent a small zero