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Technical Coarse vs Fine threads

Discussion in 'The Hokey Ass Message Board' started by Boones, Nov 26, 2020.

  1. cfmvw
    Joined: Aug 24, 2015
    Posts: 498

    cfmvw
    Member

    I've worked with a few people who didn't know the difference between a coarse thread and a fine thread, often with disasterous results.
     
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  2. indyjps
    Joined: Feb 21, 2007
    Posts: 3,991

    indyjps
    Member

    YES. I stop into different farm stores that sell hardware this way, some dont differentiate between stainless in the mix per pound.
     
  3. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,643

    Boneyard51
    Member

    My good friend told me one cross thread is worth two lock washers..... course or fine!








    Bones
     
  4. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,364

    Rusty O'Toole
    Member

    Coarse thread car nuts wear greasy jeans steel toe boots and work shirts and buy oil by the case. Fine thread car nuts wear slacks, loafers and Lacoste shirts and buy wax by the case.
     
  5. fortynut
    Joined: Jul 16, 2008
    Posts: 1,038

    fortynut
    Member

    I once read Lil' John Buttera said, more or less, having a model train set in the basement was as good a requirement as any to use 'engineer' or 'engineering' in the name of your company. I post this without any desire to cast aspersions on those who are real engineers. In making a speech, opening with a joke warms up the audience, it is said. What I came here to say is that those who wish to be wise about fasteners should add at least a couple of Carroll Smith's books to their libraries, for reference. It is also good to close with a joke. If any of you even get one of those robots with artificial intelligence and it gets a virus, you might think about giving it Robitussin.
     
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  6. winduptoy
    Joined: Feb 19, 2013
    Posts: 2,197

    winduptoy
    ALLIANCE MEMBER

    Put a different grade and thread pitch in each place you are going to attach the battery box and see which one loosens up first.
    I seem to always be at battle with engineers... I am a contractor and it always my fault

    Sent from my XT1585 using The H.A.M.B. mobile app
     
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  7. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,643

    Boneyard51
    Member

    If you are worried about a bolt coming loose, use a lock nut!







    Bones
     
  8. The general rule of thumb according to the puritans is that you cannot beat your with with a rod any thicker than your thumb. LOL

    The basics is that a part that will be assembled and disassembled on a regular basis uses course threads and a part that is seldom disassembled uses fine threads. Now this does not take into account loads and thread distortion and etc. But this is the general rule regarding the choice of course v fine threads.
     
  9. fastcar1953
    Joined: Oct 23, 2009
    Posts: 2,322

    fastcar1953
    ALLIANCE MEMBER

    I thought this was about bitch and complaining threads vs helpfull and learning threads.
     
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  10. LOL so do you think if I say something course I can a bi because it is thanks giving. :D
     
  11. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 1,620

    ekimneirbo
    Member
    from Brooks Ky

    If you want a connection that will never come loose, thread a coarse thead bolt into a fine thread nut..........better n locktite:p
     
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  12. Harv
    Joined: Jan 16, 2008
    Posts: 97

    Harv
    Member
    from Sydney

    Agree... but the answer is not that simple. The lower grade bolts have lower yield and tensile strengths, as shown in Mike's table above. Put a force on them, and the lower grade bolts deform earlier and normally snap earlier.

    However, the energy (not force) that is needed to bust the lower grade bolts is often substantially higher. This is related to the the area under a stress/elongation curve. Lower grade bolts typically have a lot more area in that graph than higher grade bolts. The low grade bolts plastically deform, soaking up a large amount of energy.

    So yes - if you put a force on a higher grade bolt for a short period of time, often the higher grade bolt will last longer. Put a lower force on the bolts for a longer time, and the lower grade bolts perform better.

    Dammit... I woz not suphosed to Enjinur any maw :)

    Cheers,
    Harv
     
    Sandgroper likes this.
  13. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,898

    gimpyshotrods
    ALLIANCE MEMBER

    If you are getting into issues of fastener longevity, you have the incorrect fastener specification, and/or an improperly engineered component, and/or the incorrect number of fasteners.
     
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  14. Wrench97
    Joined: Jan 29, 2020
    Posts: 242

    Wrench97

    I've always heard fine thread has more tensile and shear strength then coarse, coarse are easier to start, harder to strip, nick and gall.

    As far a grade 5 vs 8, Mack truck used only grade 5 hardware up until Volvo got involved in the engineering of them.
     
  15. fourspd2quad
    Joined: Jul 6, 2006
    Posts: 705

    fourspd2quad
    Member

    I agree. I pulled the front end off of my 51 woodie all the way back to the firewall and every bolt (except the chassis which I havent gotten to yet ) has been a fine thread. I was really surprised.
     
  16. 73RR
    Joined: Jan 29, 2007
    Posts: 6,467

    73RR
    Member

    ...if I thought that I was addressing a house full of like minded individuals then I would have used 'different' terminology but Engineers are a small minority on this board...
    Feel free to offer the 'right' term......

    .
     
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  17. Harv
    Joined: Jan 16, 2008
    Posts: 97

    Harv
    Member
    from Sydney

    Less so longevity, and more the type of force. If it is something that pushes and can keep pushing (unlimited energy behind it), then the high grade bolts do better. If it is something that can push then run out of ooomph (impact or intermittent force), then the low grade bolts do better - they stretch (plastically deform) to absorb the ooomph energy.

    Cheers,
    Harv
     
  18. fastcar1953
    Joined: Oct 23, 2009
    Posts: 2,322

    fastcar1953
    ALLIANCE MEMBER

    Looks like like it is turning into coarse thread. :D
     
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  19. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,898

    gimpyshotrods
    ALLIANCE MEMBER

    When you find an unlimited source of energy, do let us know.

    Until then, if the force being applied to the assembly exceeds the design specification of the fasteners, then it has been engineered poorly.

    Attempting to make up for bad design by finessing fastener grade is just plain sad.
     
  20. anthony myrick
    Joined: Sep 4, 2009
    Posts: 6,631

    anthony myrick
    Member

    When it come to suspension I use a factory bolt.
    All my suspensions have factory hardware. Sometimes hard but doable. I have even made trips to the boneyard to just locate bolts.
    As a professional, all damaged or non reusable bolts gets a factory bolt.
    I was installing a bolt in cage once. The cage came with grade 5. Grabbed bolts from our grade 8 bin. Was told to check the rule book. Rules specified grade 5.
    As far as thread count, it depend on a few things. Thickness of material is one. I use fine threads when adding threads for fuel or brake lines to a chassis. But you will see the factory use screw threads for stuff like this.
    Just general stuff, like body panels, I use grade 5 standard thread stuff.
    But I’m also the crazy person that will reuse every dang bolt I can. My friends look at me crazy as I soak old bolts in rust removers or sandblast em.
    I pay attention to what the factory used. If they used a fine thread bolt and lock nut, then I try to duplicate that. If it’s corse and a lock washer, then I duplicate that.
     
  21. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,898

    gimpyshotrods
    ALLIANCE MEMBER

    Fine.
     
  22. Marcosmadness
    Joined: Dec 19, 2010
    Posts: 363

    Marcosmadness
    Member
    from California

    Squirrel is right (again) that the aviation industry (including the USAF) use fine threads almost exclusively. The exception seems to be the reciprocating engines.
     
  23. What Jim said.....sure seams to be a lot of that in early pre war and after the war (surplus) that was fine thread - was just demo-ing a 1960 Chevy and still a lot of fine and not some much coarse stuff.
     
  24. Country Joe
    Joined: Jan 16, 2018
    Posts: 263

    Country Joe
    ALLIANCE MEMBER

    I was going to post something similar. Now, I didn't stay in a Holliday Inn last night but, I notice when taking apart anything suspension related, it's almost always fine thread.
     
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  25. Budget36
    Joined: Nov 29, 2014
    Posts: 4,848

    Budget36
    Member

    Screw it then....
     
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  26. Rickybop
    Joined: May 23, 2008
    Posts: 6,751

    Rickybop
    Member
    from Michigan

    Ahhhhhhhh...
    Nothing like sitting around the fireplace after a nice Thanksgiving dinner with friends and having an engaging (2.5 X dia.) discussion on the pros and cons of coarse vs fine thread fasteners and the like.
    Better 'n football.
    Of coarse, I hope you all had a fine Thanksgiving. :D
     
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  27. squirrel
    Joined: Sep 23, 2004
    Posts: 47,168

    squirrel
    Member

    Yes, we had a fine 3 coarse dinner.
     
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  28. anthony myrick
    Joined: Sep 4, 2009
    Posts: 6,631

    anthony myrick
    Member

    I had a great 8 course meal today
     
    56don likes this.
  29. Lloyd's paint & glass
    Joined: Nov 16, 2019
    Posts: 3,245

    Lloyd's paint & glass
    ALLIANCE MEMBER

    Screw this :rolleyes: of coarse, I'm out of puns
     
    anthony myrick, 56don and fastcar1953 like this.
  30. blowby
    Joined: Dec 27, 2012
    Posts: 7,056

    blowby
    Member
    from Nicasio Ca

    Fine thread bolts have a larger minor diameter, something around 25 thou on a 3/8s bolt, so there is that. But being the same major diameter, the threads aren't as deep as coarse, of course..
     

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