I am working on changing a machine design from metric to US standard; however, I am vague on what sizes are harder to find than others. Ive been told the 5/16" thick plates Ive been using are tough to find, to replace the 8mm thick plates currently used. Same for the 5/8" plates to replace the 15mm plates. Also, when I use tubing (say, 5"x3") and the thickness is 8mm or 15mm, I've been using 5/16" or 5/8" respectively again. Are these sizes uncommon? Is it mostly 1/8", 1/4", 3/8", 1/2", and 3/4" that I should be using? Cost is an issue in getting this project greenlit, but I'm also worried about everything fitting together, and adding too much weight on the motors by changing size.