[ Ref. 240105 MMDigest, Flat Steel Bar Stock For Player Pianos ]

This material used to be listed in McMaster-Carr as "flattened wire".
Apparently it was made by flattening round stock in a rolling mill,
which gave it the rounded edges.

Bill Klinger
Flippin, Arkansas
http://www.klingerorgan.com/ 

 [ Also known as flattened tape, it is used as a material for
 [ the manufacture of springs, saws, bushings of motorbike chains,
 [ rollers, rolling bearings and frames for upholstered furniture.
 [ Source: https://metiz-brovary.com/en/flattened-wire/ -- Robbie