Help with drill sizes please!

Discussion in 'Other Trades Talk' started by Cpyne, Jun 25, 2005.

  1. Cpyne

    Cpyne New Member

    what size drill bites do i need for say a M8 bolt?

    Is there a convertion i need to know?

    Thanks

    C Pyne
     
  2. Dewy

    Dewy New Member

    Clearance drill? 8.2mm 21/64" Letter P
    Tapping drill? 6.8mm 17/64" Letter H

    Imperial sizes are nearest
     
  3. Cpyne

    Cpyne New Member

    Thanks or that, can ask where you got thoses from? The holes are for choach botls so all the holes have to be clearance.
    Do you kow that size drill bit is needed for M12?

    Thanks
     
  4. PowerTool

    PowerTool New Member

    Metric sizes are the diameter of the thread - so M12 is 12mm outside diameter on the threaded part.
    So in this instance,something slightly larger than 12mm (e.g. 1/2 inch/12.7mm) or use 12mm drill bit,and when you have drilled the hole,just run the drill bit in and out a couple of times to make sure the hole is clean.
     
  5. Hitch.

    Hitch. New Member

    It depends on the application of the bolt.
    As dewy says, M8 is the diameter of a metric bolt...(M4,5,6,8......)
    For coach bolts id just use a drill the same size and make sure the hole is clean. This will ensure the square shank will grip the wood. If the bolt is going through steel aswell, drill the steel to a slightly larger hole, 8.5 or 9mm.

    In the metal fabrication world, we tend to drill/punch our holes larger, say a 26mm for 24mm bolt, this will allow some movement making the putting together and alignment much easier.
     
  6. Hitch.

    Hitch. New Member

    I meant to say Powertool there...
     
  7. Dewy

    Dewy New Member

    When imperial was all we had the recommended clearance was 1/64" larger for the clearance drill.
    I usually used 1/32" larger for bolts.
    Metric recommend ·2mm larger even though that is only 8 thou.
    I'd be inclined to use ·5mm larger for clearance.
     
  8. Stoday

    Stoday New Member

    Measure the diameters of your bolts.

    I have some M8 bright galv bolts & they are 7.9 mm dia. Similarly with M10's, somewhat under 10mm dia.
     

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