bolt sizes - help needed

rodgers73
rodgers73 Posts: 2,626
edited December 2012 in Workshop
I need to order some bolts from eBay but I'm not sure on my sizing.

Using some vernier callipers I can tell that the diameter of the thread is 15ml - does that mean I'm looking for M15 bolts?

Or am I on the wrong track here?

Comments

  • sungod
    sungod Posts: 17,413
    yep, metric fasteners are sized by the thread diameter

    aside from size, there are also different grades, materials etc., if it's safety critical, make sure you select the correct grade for your application

    there's a handy explanation here...

    http://www.boltdepot.com/fastener-infor ... Chart.aspx
    my bike - faster than god's and twice as shiny
  • Monty Dog
    Monty Dog Posts: 20,614
    If they're 15mm diameter, that's a pretty hefty bolt for a bike? Also consider it could be a 5/8" imperial thread of which there are a number of different thread forms i.e. UNC, UNF, Whitworth plus others. Suggest you visit a local engineering fastener supplier to check.
    Make mine an Italian, with Campagnolo on the side..
  • centimani
    centimani Posts: 467
    Is that a crank retaining / preload bolt ?
    The only place on a bike where you may find a bolt anywhere near that size. If its not on a bike, its still an odd size. If they're digital calipers, did they zero with the jaws closed (i have a pair that require zeroing every time)
  • rodgers73
    rodgers73 Posts: 2,626
    Sorry, my mistake - just re-checked the measurement. I'd forgotten to reset callipers to zero! Bolt is 3.75mm wide so I'm guessing an M4 bolt does it?
  • freezing77
    freezing77 Posts: 731
    rodgers73 wrote:
    Sorry, my mistake - just re-checked the measurement. I'd forgotten to reset callipers to zero! Bolt is 3.75mm wide so I'm guessing an M4 bolt does it?

    Are you sure you should be doing this?.


    Not knowing the difference between 4mm and 15mm is kinda worrying for someone carrying out any sort of mechanical assembly
  • rodgers73
    rodgers73 Posts: 2,626
    My garage is cold and I was in a rush the first time. The bolt is to tighten my SPD release mechanism. Hardly a life threatening aspect to my riding.

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