I currently projection weld on to several types of high strength steel, but I am having problems with one specific application. I am projection welding a 7/16 nut and an 8mm nut on to a bracket made out of SPFH 590 material. The 8mm nut has broken or fallen off on several occassions, but the 7/16 nut has never broken or fallen off. They are welded on the same welder, but with different transformers that cascade when fired. They are both under Ohma cylinders and have separate settings in the panel. I did a weld lobe type model to come up with the current settings with the outcome being based on rotational torque versus expulsion. I am fairly confident that the weld parameters are within an acceptable range. I am using a Centerline tip unit on the bottom and top. The grounding is the same and I have monitored the secondary current flow through both tips and it is very consistent. The only difference I see is in the size and shape of the weld projection. The 7/16 nut has a .8mm to 1.0mm and the 8mm has a .6mm to .8mm projecton. I tried a different 8mm nut with a .8mm to 1.0mm projection and it increased the point of breakage in the rotational torque by over 40 ft/lbs. This was welded at the exact same parameters! Should the weld projection size be larger for high strength steels or is there something I am missing?