I need to drill a hole in metal for a 0-80 screw. So I bought a tap labeled 0-80. Then I looked at this chart: https://homerepairgeek.com/define/tap-drill-chart.html. I think it says to use a #50 or 52 drill bit, so I bought a #52. However after I drilled a hole with the #52 bit, I found that the hole is too large for the 0-80 tap. Did I do something wrong?

  • 3
    You went all the way over to the 'Pre-drill Size' columns instead of stopping at the 'Tap drill size'. You should be using a 3/64 or #55 drill.
    – brhans
    Commented Jan 7, 2021 at 3:43
  • 3/64 matches with my chart or .0469 were you looking at a clearance drill?
    – Ed Beal
    Commented Jan 7, 2021 at 14:26
  • Is the "tap drill" the thing that makes the threads or the drill bit used to make a hole first?
    – user348514
    Commented Jan 7, 2021 at 15:09
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    The "tap drill" is used to make the pilot hole. Then you tap the hole to cut the threads for your screw.
    – FreeMan
    Commented Jan 7, 2021 at 16:16
  • 2
    The linked page is long, tedious, and poorly written, so I'm hardly surprised you understood that wrong, given what they wrote. "Getting Your Pre-Dilled Hole to the Right Size The last segment of the tap drill chart are the columns on the right third of our table. This is the clearance drill size conversion, or the more plainly, the size drill bit you need to cut your initial hole before carrying out the rest of your tooling." Easily read to mean "the hole you'd pre-drill before tapping" and that's because of poor writing/word choice.
    – Ecnerwal
    Commented Apr 15, 2022 at 2:01


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