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Diameter of imperial machine screws

  1. May 2, 2009 #1
    Dear Forum,

    I am currently trying to buy some imperial machine screws and bolts online, and I am confused with how the diameter is given.

    The website I am seaching (boltdepot.com) gives me these diameters but I don´t understand what is meant by i.e. "2-56"

    2-56
    4-40
    6-32
    8-32
    10-24
    10-32
    12-24
    1/4-20
    5/16-18
    3/8-16
    1/4-28

    Can anyone help me? I am specifically looking for a 5/32 inch diameter screw but this does not appear here. Anyone suggesting a different good site for buying fasteners online, preferably located in europe?


    best regards
    t.
     
  2. jcsd
  3. May 2, 2009 #2

    mgb_phys

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    Below a 1/4" they are just given numbers, a #8, #10 etc - the diameter is d=0.06" + (#*0.13")
    or you to look up the diameters in a machinist handbook
    Above 1/4" the first number is the diameter of the bolt in inches.

    In both cases the second is the number of threads per inch, so a 'quarter-20' is 0.25" diameter and a thread pitch of 0.05"

    5/32 isn't a standard US size, it's almost a #7 - which is also rare.
    Is this an old British part ? in Which case it might be whitworth.
     
    Last edited: May 2, 2009
  4. May 2, 2009 #3
    Thanks,

    It is definitely an US part.

    My local store here thought it was a 5/32 and I believed them. Might even be a #7 as you say. I probably need to measure it myself....

    Edit:
    With respect to the list in my first post, does 2-56 then mean screw #2 with 56 threads per inch? and "4-40" is #4 with 40 tpi?

    regards
    t.
     
  5. May 2, 2009 #4

    mgb_phys

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    Correct - I clarified my post a little
     
  6. May 2, 2009 #5
    Thanks.t
    This helped a lot.

    t.
     
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