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MJC

In article ,
says...

Those fingers are spring bronze, very thin and relatively hard to
duplicate as the bronze alloy is a delicate balance between being too
hard and not having enough spring. Too hard would eat into the
commutator, not hard enough would anneal and fail quickly.

Back in the 1950s (I guess) when my Dad and I were playing with toys, we
also thought that a small motor had phosphor-bronze spring brushes.
Having no idea where to get stock metal we tried cutting up slices from
a roll sold by a local hardware as draught-prevention seals for doors
etc. I don't remember how durable it was!

Not sure if it is the same stuff, but I have some more recent "Atomic
Weather Strip" made of "specially prepared copper alloys" and carrying a
ten year life time...

Mike.