[robz71lm7]

So a certain student's machine design professor has pushed the idea into people's heads that we should use SAE Grade 5.2 or greater for all thing structural or important. Good luck finding those bolts, I knew they existed, but have never seen any. His logic is that the yield strength of a grade 5 bolt changes when you get over a certain diameter (1" IIRC) whereas the 5.2 grade's yield strength is constant. We also had a machine design project where we had to specify a size and preload for a grade 7 bolt. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/rolleyes.gif) Also according to him, nobody makes bolts with cut threads any more. Aren't most cheap chinese bolts manufactured with cut threads?

[pknowles]

about the rolled threads...i have no clue. never even heard of them

Instead of using a die to cut the threads they use small rollers that deform the materal into shape to form threads. Rolled thread are stronger then cut threads, but cut threads are cheaper and sometimes quicker to make.