Three types of AAR axles are used under freight and passenger cars. The first is an early designed solid
axle used with friction bearings; it has a collar inside of each wheel seat called the black collar. The second
type, designed in 1940, has no black collar but has a raised wheel seat and is used with either friction or roller
bearings. The chief difference between the two is the way the journal is designed. The third type is a tubular
axle and may be used with either friction or roller bearings. These axles and their new dimensions are
explained in paragraph 2.16.
Markings on axles are made by cold stamping them in letters not less than 1/4 inch high in one of three
ways. On friction-bearing journals used under freight cars, the markings are made on the face of the end collar;
on roller-bearing journals used under freight cars, the axles are marked on the journal end. Markings on axles
used under passenger cars having roller bearings are made around the outer rim of the journal end. Each of the
three ways of marking axles is shown in figure 2.24. The numbered notes in the legend are explained in the
following subparagraphs (there are no notes numbered 2 and 5).
a. Laboratory acceptance stamp--Note 1. The steel in each heat or group of axles is laboratory tested for
chemical composition and physical properties. If the steel meets the AAR specifications, the axles are stamped
b. Manufacturer's name or brand--Note 3. If, for example, the patented trade name for Raleigh Associated
Steel Company was RASCO, these letters would be stamped as shown just below the date.
c. Date--Note 4. The month and year that the axle was made is shown. For example, if an axle was made
in September 1964, the numbers 9-64 would appear.
d. Grade of axle--Note 6. Axles are of three grades designated by the letters U, D, and F. The letter U
indicates that the axle is untreated (not reheated); D indicates that the axle has been through an annealing
process; and F means that the axle has been normalized and tempered (reheated and re-formed to standard
e. Heat number--Note 7. Each ladle of molten steel is called a "heat" and given a number. All axles made
from this one