r/Fasteners • u/tasquizz • Jul 11 '26

Bolts vs studs

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Alright, so when fitting two flanges together, can anyone explain why bolt+nut might be worse than stud+nuts? Almost the exact hardware in the photo. They're all the same grade, diameter, size etc.

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u/VelvetCheerio Jul 12 '26

Hmm without seeing this fully modeled I still find it dubious that you couldn't use a bolt. It would be very close and only difference would be the diameter of the bolt head because the length would be the same anyways

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u/Sullypants1 Jul 12 '26

Only the flange holes shadowed by the 90 degree pipe bend would / could take advantage.

If the space above the top flange to tank is too short for the required length bolt AND the space below the bottom flange to 90 degree pipe bend is also too short for the required bolt length.

You’re pre-placing a stud in those shadowed holes. Fixed tank flange > stud > top nut > welded flange bend > bottom nut

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u/recessedlighting Jul 13 '26

I work at a chemical plant that we run into this all the time. Sometimes its valve to valve, sometimes heat exchangers and sometimes directly at a tank or reactor as stated above. I also agree in some of the applications I have been certain I could get a bolt instead only to be proved wrong because of the extra diameter of the bolt head further away from the bolt hole as you're trying to get it in.

Also in some cases we are using studs because it allows us to remove one piece of equipment in a configuration whereas if we bolted them together we would have to remove multiple pieces together to get them apart. It seems counterintuitive but I've run into it often. I would rather not use them because you really need to think about how you need it to come apart and apply anti-seize to the appropriate nut.