Replacing stem bolts
Most bolts should have their tensile range marked on them somewhere, often stamped inside the hex cap. There should be a short number - 3.6, 8.8 etc.. Even a fastening rated as low as 3.6 is capable of 27 tons per square inch, more than 300n per square meter. A stainless steel M6 can probably handle 1.25 tonnes, the aluminium you're bolting into / through will fail before that.