Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Problems understanding imperial hole sizes

  1. Oct 6, 2009 #1
    We need to manufacture a structural component, but we do not understand the imperial hole dimensions given on the drawing:(we went metric in South Africa in the 1960's)


    We think it may describe the bolt and not the hole, but are unsure what it means.
    Can anybody help?
  2. jcsd
  3. Oct 6, 2009 #2


    User Avatar
    Science Advisor

    Is that for a clearance hole? That call out makes no sense. Please describe the hole function and where it is on the part. I'm sure we can decipher it.

    If it is a clearance hole, perhaps, since [tex]\frac{29}{16} + \frac{1}{8} = 1 \frac{15}{16}[/tex]
    that they mean simply a 5/8 diameter hole by 1-15/16 deep. I'm really reaching there. More info would really help.
  4. Oct 6, 2009 #3
    Perhaps the -1/8" indicates a tolerance range (+0/-0.125)?
  5. Oct 7, 2009 #4
    The hole is to be punched through an unequal angle 64mm x76 mm x 6mm (Electrical substation structure being maintained) .

    We think the dimension refers to the bolt, namely:

    5/8" (diameter) x 29/16" (length) - 1/8" (Pitch?) and that a generic tolerance on the hole is applied.

    Does this make sense?
  6. Oct 7, 2009 #5
    Standard thread pitch for 5/8" diameter fasteners is 11 tpi, or 18 tpi (threads per inch). Less common is 24 tpi.

    I believe the -1/8" spec is a tolerance for the bolt length.
  7. Oct 7, 2009 #6
    Maybe the 29/16 is really 2 9/16 ie, two and nine 16ths inch. Why anyone would write 29/16 instead of 1 13/16 is beyond me.

    as for the overall question, I have no idea. 2 9/16 inch would be 2.5625 inch or 65.0875mm; maybe that corresponds to your 64 mm? (I mean 64 mm to the nearest 1/16 inch)
  8. Oct 7, 2009 #7


    User Avatar
    Science Advisor

    Is there any way that you can scan in the print section that has the hole call out? It would sure help. I definitely like the idea of the .125 being a thread length tolerance call out although it follows no drawing standard I have ever seen.

    There are a few things that worry me about the callout:
    1) If it is a clearance hole for a 5/8-11 or 5/8-18, then a 5/8 diameter hole will be too small for a clearance hole.
    2) If you take the -.125" for the bolt length tolerance, then the bolt will not be long enough for the angle. Even with the full length, there is no room for a nut.
    3) If the hole is going through a piece of angle, why do you need a hole that deep? You should only need a depth equal to the thickness of the section, i.e. 6 mm.

    This is why it would be nice to know exactly waht is going on around this callout.
    Last edited: Oct 7, 2009
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook