These seem to work well with the 6"x1/2" pine boards I'm using on them, with only a few pictures of knick-knacks worth of weight on them. I don't think these would hold much more weight than you see pictured before they'd start to bend.

Print settings: 

• Push Plastic PLA
• .3 mm layer height
• .4 mm nozzle
• no supports needed
• printed on SOVOL SV04 (IDEX)

I painted mine with a spray-paint like this one, which is designed to produce a metal-looking finish, and partially hides the layer lines:
https://www.walmart.com/ip/Rust-Oleum-Hammered-Spray-Paint/17011159?athcpid=17011159&athpgid=AthenaItempage&athcgid=null&athznid=si&athieid=v0&athstid=CS004&athguid=-7dDb7J6hvi-8HiBlQKL0b3VeMBt1eqo7liU&athancid=null&athena=true