[ Source of low-carbon steel bars with rounded edges: ]

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

Don Teach
Shreveport, Louisiana

 [   rectangular bars with rounded edges (catalog page)
 [ http://www.mmdigest.com/Attachments/20/02/24/200224_052820_Img_6904a.jpg 
 [   lever
 [ http://www.mmdigest.com/Attachments/20/02/24/200224_052820_Img_6908a.jpg 
 [   lever
 [ http://www.mmdigest.com/Attachments/20/02/24/200224_052820_Img_6909a.jpg 

 [   switch, fixed piece with mounting screws
 [ http://www.mmdigest.com/Attachments/20/02/24/200224_052938_Img_6905a.jpg 
 [   switch, side view, sliding piece with hole for brass tube
 [ http://www.mmdigest.com/Attachments/20/02/24/200224_052938_Img_6906a.jpg 
 [   switch, sliding piece with hole for brass tube
 [ http://www.mmdigest.com/Attachments/20/02/24/200224_052938_Img_6907a.jpg