Drill size metric converter

Discussion in 'Getting Started' started by Topo, Jun 18, 2004.

  1. Topo

    Topo Member

    Used to metric measures, I always struggle when find references to inches and so, having to resource to the calculator. :rolleyes:

    But if we are speaking about #s of screws, drills, and so, I'm completely lost!
    What is a tap 56-2? :confused: How many millimeters are a drill #50??? :confused: :curse:

    It was a pity, because in the net there is a wealth of information written by fellow US & english modelers that work with imperial measures. :cry:

    Enter the internet wonders: The drill size table & converter!! :D :D :D


    My «calculator days» are gone now, and I wanted to put this link here. Maybe another «metric guy» find it of use! ;) :thumb:

    Oh, I forgot to mention: in this link there is a BUNCH of other calculators, converters & tables! :eek: :p
  2. 60103

    60103 Pooh Bah

    The National Coarse/National Fine screw sizes have 2 parts. First is the size of the screw -- the diameter of the rod. The second is the number of threads per inch.
    And a 2-56 screw is a coarse thread!
  3. Russ Bellinis

    Russ Bellinis Active Member

    What is really confusing is that a 2-56 is not metric. The U.S. uses two different drill size standards. There are fractional sizes, and then there are number sizes. I think the number sizes are a result of the SAE. Automotive engineers needed more sizes than fractional sizes offered. How the sizes were established I don't have a clue.
  4. RailRon

    RailRon Active Member

    Javier, thank you very much for this link. This is an outstanding collection of tables and calculators! :thumb:

    Now if I only had an internet connection in my workshop... :( :D

  5. 60103

    60103 Pooh Bah

    I just had a look at the table. The wire sizes there are not related to the size of screws. In the screws, the numbers go down as the screw gets smaller; in wire sizes the numbers go up as the wire gets smaller.
  6. Topo

    Topo Member


    Humm, I see... So 2-56 stands for 56 threads per inch, but what unit is the "2"? millimeters? inch fractions?

    (BTW, in my first post, I wrote "56-2". Sure that this is a really weird screw!! :eek:
    What a "typo" I made!! :rolleyes: )

    Rats! So I'm still without a good table relating the screw # sizes to their metric measures... :(
    When I find his table I noticed that the header says "Wire No./letter", instead of "Screw No." or so, but I supposed -mistakenly- that they were the same, because the table is about drills.
  7. 60103

    60103 Pooh Bah

    56-2 would be about 20 cm across and 2 threads per inch (or 12.5 mm pitch) !
    I'll see if I can find a table -- most of mine are on paper,
  8. Russ Bellinis

    Russ Bellinis Active Member

    To add even more confusion to the issue, you need to use a #45 drill bit to get the right sized hole for the 2-56 tap, and I think if memory serves that the clearance drill size would be a #50.

Share This Page