A bolt is a bolt is a bolt?

Discussion in 'Mechanic and Repair' started by gogetter, Jul 31, 2002.

  1. gogetter

    gogetter Banned
    Posts: 3,256

    Wasn't sure where to post this one.
    Anyway, I just had to replace the blade bolt and nut on my mower. It ran me about $12 to get exact replacement parts from the dealer.

    Out of curioisty stopped at hardware store and found same SIZE nut and bolt, BUT, different threads for about $4.

    So question is, do the type of threads or thread count matter and if so, why?

    The replacement parts had a higher thread count then the nut and bolt at hardware store.
    How important are the threads?
  2. Look at different hardness of the metal in the bolt.
    hash marks on the head of the bolt define hardness of metal, I don't remember exact system but no marks = soft metal, more marks= hard
    Since the bolt is in a critical area I would make sure that replacement is same quailty.

    If its a nut and bolt then using a fine/coarse thread wouldnt matter
  3. gogetter

    gogetter Banned
    Posts: 3,256

    Thanks Bob, I did see marks as you mentioned. I was wondering what they represented.
    Hadn't thought of the 'hardness' factor. Thanks again.
  4. Lohr Equipment & Wel

    Lohr Equipment & Wel LawnSite Member
    Posts: 17

    As far as I know if you add 2 to the number of lines on the head of the bolt,this will give you the grade of bolt.Example,three lines add 2,that is a grade 5 bolt,6 lines add 2 that is agrade eight. This is just my personal opinion but I spend the extra money and buy good American Grade 8 bolts for everything.If it ain't made here I don't want it.
  5. sdwally

    sdwally LawnSite Senior Member
    Posts: 385

    Grade 2 or lower - no marks
    Grade 5 - 3 marks
    Grade 8 - 6 marks
    There are also higher grade bolts with other markings. A good quality bolt will also have a manufacture's id mark on it also. Without the manufacture's id, you can not be sure of an acurate grade rating. Grade 5 is the standard for normal use. Grade 8 have the applications, but can be to brittle for use everywhere especially if it has a shearing force applied to it.
    TPI(threads per inch) have different torque ratings. The more TPI the higher the torque rating. Depending on the application, national coarse(NC) is more widely used, however a national fine(NF) can be substituted with out any problems normally. Metrics come in standard, fine, and extra fine TPIs. Most widely used are standard and fine TPIs.
    Metrics are rated also using a different identifiers. 8.8, 10, and 12 as I recall. The standard rating depends on the sized bolt to be used. They also should have a manufacture's id mark.
  6. bob

    bob LawnSite Platinum Member
    from DE
    Posts: 4,254

    What kind of mower is the bolt from?
  7. edward hedrick

    edward hedrick LawnSite Senior Member
    Posts: 871

    I worked for a local Industrial hdw store. Sold 5/8x11x9" grade

    5 for $2.50. Local Scag dealer bought from us sold it for $10
  8. The Mowerdude

    The Mowerdude LawnSite Senior Member
    Posts: 372

    Hey, Edward

    I think that's a little scary, because all of my Scags and Great Danes came with grade 8.

    I'm glad you told me that. In the future, I'll be more aware of what I'm buying.
  9. gogetter

    gogetter Banned
    Posts: 3,256

    Bob, it's my 36" Exmark metro. This is the second bolt/nut I've stripped somehow. They went on fine, but wouldn't come off. Think I may have over tightened them.
    Ordered a torque wrench the other day.

    Thanks for all the info in the replies guys. Interesting stuff.

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