I am trying to attach pieces of 2-by wood to the frame tubes of a conex shipping container. The steel is about 1/8" thick. I probably need screws at least 1/4" diameter to get the strength I need (100+ lbs shear).
Found this fairly comprehensive article about all the different types of sheet-metal screws:
... and they say you need "thread cutting" (aka. "Type F") instead of "thread forming" for "thicker and harder" materials.
My question is: would 1/8" thick steel (I'm assume it's mild steel in a ubiquitous thing like a shipping container, and it wasn't that hard to drill through) be consider a "thicker" material, or will an ordinary #14 sheet-metal screw suffice ?
An ancillary question: If ordinary sheet-metal screw is unsuitable as I expect, will a "self drilling" type such as:
... work ? I would likely drill a pilot hole anyhow, and use these as thread-cutting type. The self-drilling seems easier to find than thread-cutting.