Question : What grade of bolts to hold tow hooks onto frame ?

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by JTward1, Feb 21, 2013.

  1. JTward1

    JTward1 Rockstar Gold Member 100 Posts

    I'm installing a RPO addition to my 1990 1500 Silverado and the hooks go through the frame and into two 1/2 " steel threaded blocks. But I don't know how strong they need to be. Grade 5 or 8 ? Thank you !
  2. aloxdaddy99

    aloxdaddy99 Epic Member 5+ Years 1000 Posts

    I would go with 8. The last thing you want to happen is have a bolt failure will using the hook.
  3. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

  4. trentkoger

    trentkoger New Member

    Wow 1/2 inch seems a little small considering the application. But i guess you would want them to fail before anything else.
  5. j cat

    j cat Epic Member 5+ Years 1000 Posts

    a grade 8 bolt is good for 20,ooolbs with a 13 thread. threading into a plate ? what is the plate/block grade and material ?

    using grade 8 bolt/nut would be best torque to 80 ft LBS... 20,ooo lbs would be a straight pull clamp rating. shear rating would be much lower.
  6. JTward1

    JTward1 Rockstar Gold Member 100 Posts

    I went to Home depot and there's no standard grade of bolts that fit the screw block that LMC truck supplied. So I went Pep boys as they carry automotive fasteners, and I got 7/16-14 bolts but they seem a little loose, So I'm not sure i got the right bolts, do you think it's metric fastener ?
  7. j cat

    j cat Epic Member 5+ Years 1000 Posts

    the 7/16 bolts should not be correct . a 7/16 -14 will thread loose into a 1/2-13 thread. could be it is metric if the 1/2 -13 does not thread. did you try a 1/2 -20 thread ? the 20 thread would be a better thread for this app.

    with the plate in hand you should be able to find the proper hardware. homedepot is not the place to go to find quality hardware. see if a hardware store in your area has a full selection of fasteners.

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    I would purchase the correct bolts from LMC truck . that is the safe way to handle this.
  8. JTward1

    JTward1 Rockstar Gold Member 100 Posts

    Yeah, I did that. I don't have any good fastener nuts& bolts shops anywhere near me.
    Last edited: Feb 24, 2013
  9. j cat

    j cat Epic Member 5+ Years 1000 Posts

    use a torque wrench to secure bolts. if you use too much torque then the load you have to handle will be reduced .

    if the bolts you get have no torque value look up what grade bolt they gave , and see what the low end torque should be used to secure them. you do not want to stretch the bolts to the max , when securing.
  10. FrigginNoodles

    FrigginNoodles Epic Member 5+ Years 500 Posts

    When I installed my snowplow mounts I used grade 8 and a tourque wrench for everything, including replacing the tow hook bolts. I was able to purchase the, from tractor supply. Hopefully you have one nearby.

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