Can some one help me figure lifting capacity for this spreader bar?
You have not specified the direction of the loads applied to the four bottom edge holes.
I see three potential modes of failure.
1. The top hole pulls out.
2. The bottom holes pull out. This will depend on the direction of the loads suspended from the bottom holes.
3. The plate may bend about the mid-line, through the top hole, due to compression in the lower edge. Again it is dependent on the load direction. Maybe you would benefit by welding a flat along most of the bottom edge to keep it straight and prevent the plate folding.
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