Makes a good ground, but not a very strong clamp
I bought this to hold steel for welding and found it to only be so-so. 2x2x.125 A500 steel tube in only 36 inch length would break free with very little bumping. I was surprised how well it works for a ground. When I used it on 1/8th inch hot rolled steel, it was a great ground point for Plasma cutting and welding. As far as strength, I was able to easily pull it free from 1/8th inch steel without any twisting. The magnetic force is not anywhere close to 150 pounds. Found it to be about the same holding force as the large red magnets in my pictures.
ProsSurprisingly good ground
ConsNot very strong