I bought some steel to shim my MII crossmember between the frame rails tightly. Once I bought the steel plate I started wondering if I should be using cold rolled for this or does it really matter. Also how can you tell if it is cold rolled or hot rolled steel?

 

The material for a shim doesn't matter. Cold and hot rolled have essentially equal compressive strengths.

Cold rolled steel has a smooth silvery finish to it. Hot rolled steel has a scale on its surface and is gray in color.

 

What he said.

 

I think I got cold rolled. When I was grinding it last night it did have a silvery finish to it. I'll have to look again when I get home. Would hot rolled be fine for boxing the frame? Also what thinkness is recomended for frame boxing?

 

Generally speaking, cold rolled is MUCH easier to find in sheet stock. Hot rolled is more common as thicker plate and extruded shapes, such as structural channel, angle, H-beams, etc.

1/8" thick cold rolled sheet is preferred for frame boxing, since that is what the frame channel was made from.

So, if you were able to find hot rolled sheet to use to box the frame, you would need to grind the face of it to remove the scale so that the finished product looked decent, but the strength of the hot rolled box plate would be the same as the easier to find cold rolled sheet.