Greetings automuse,  Since it hasn't been said yet, motor brushes
are not as simple as they appear.  I have a few books on motor repair
and rewinding and read them at one time, although I have never rewound
a motor myself.

As is often the case where situations seem to be simple, there are
hidden complexities.  The composition of motor brushes varies according
to size and design of the motor.  A brush for one application may not
suit another and may cause significant damage due to arcing.  Motor
speed, size, commutator design, developed power and probably several
other variables that I forget, all contribute to different brush
requirements.

As inviting as it is to take a massive brush from a generator or other
source, or a welding rod and cut it down, this may create a situation
in the motor that can cause considerable damage.  This is especially
bad if the motor is an antique and the damaged parts will be difficult
to replace.

As I recall, the brushes originally mentioned in this thread were for
a start switch.  To me, this sounds like a less critical application
than DC or universal motor brushes but there still may be some
application specific requirements.

So, if you are going to rework a motor brush to replace one that is
not available, it is my suggestion to start with something as close as
possible to the original in terms of motor size, power, speed and basic
design.  Better yet, turn the job over to a professional who knows
what to do.  There are literally thousands of motor brushes available
and there are people who know how to use them.  Eurton Electric in
California sell parts as well as repairing and rewinding motors of all
sorts, including brush motors that cost many thousands of dollars and
which have to be done right.

Best regards,
Spencer Chase
Laytonville, Calif.
http://www.spencerserolls.com/