Often I need to make brackets for use in a player piano. The steel
with the rounded edges is not a hardware store item. All the brackets
in player pianos, from Seeburg nickelodeons to Standard Action players,
used this steel.

https://www.mcmaster.com/products/flat-steel-bars/low-carbon-steel-bars-with-rounded-edges/ 

Don Teach
Shreveport, Louisiana

 [ A similar steel source is
 [ https://store.buymetal.com/carbon-steel/rectangular-bar.html?bm_material=31 
 [ -- Robbie