I checked all of the hardware stores in my area and I can buy 1/32 (~ 0.79mm) and 3/64 inch (~ 1.2mm) drill bits. No source in my area carries bits which are between those two sizes which would then be the perfect hole size for various pin headers (like the IDC plugs).

Rather than me wait 4+ weeks in hopes that I can get sufficient perfect drill bits online at the right price (from china?), I'm looking for another feasible (if possible) way to make my own sufficient size hole for the IDC plugs to fit in. I tried fitting them in a 1/32 inch hole and that doesn't work. If I use 3/64 inch, the plug fits loosely and part of the supporting track is gone due to the hole size. That's why I'm interested in a hole size that's in-between, something like 1mm in size.

The only thing I could think of which can rather be dangerous is to use a mini motorized drill and move the motor so the drill (while it's spinning) is at a 20 degree angle relative to the board itself and then keep adjusting the motor so that the drill points at every direction at some point. Another drawback to this method is that the drill bits can easily break.

I also looked into sawing the PCB with the drill bit. I managed to do this before with bigger drill bits when I didn't have the tools in order to create the support holes for the serial port. But I'm afraid if I do this with small bits, I'll break them.

So my question is, other than waiting 4+ weeks online for a chance to receive drill bits in the mail after ordering them, is there a good way that I can use to create a 1mm hole given that the closest bit sizes available to me are 1/32 inch and 3/64 inch?

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    \$\begingroup\$ Where are you located? In the US McMaster-Carr carries bits of all sizes and has reasonable shipping. Amazon will ship to Canada and probably carries what you need as well. \$\endgroup\$
    – BobT
    Apr 2, 2017 at 22:06
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    \$\begingroup\$ Drill bits that small are incredibly easy to break as I found years ago. I'd try drilling through with the smaller one and then as far through as I could with the large one without going through. Then push the connector through the last bit by hand. But as @BobT says, I'm sure you could hold of the right size quicker than 4 weeks. Check the connector datasheet, they should have details on pin/hole sizes. \$\endgroup\$
    – Finbarr
    Apr 2, 2017 at 22:24
  • \$\begingroup\$ Make the annulus of the hole large enough to take a 1.2mm drill bit. \$\endgroup\$ Apr 2, 2017 at 22:32
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    \$\begingroup\$ You may need to visit a hobby store not a hardware store. \$\endgroup\$
    – Trevor_G
    Apr 2, 2017 at 23:21
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    \$\begingroup\$ There's a standard plastic pack of small number-sized wire twist drills all the usual importers carry, they're not great but will work in phenolic and are cheap to replace when broken. You should be able to get them in a few days - actually saw a packaged offered retail yesterday. \$\endgroup\$ Apr 3, 2017 at 0:12

2 Answers 2


The best way to drill such a hole, is with a suitable twist drill.

The "IDC connectors" possibly have the familiar 0.025" square pins, and those will fit any hole larger diameter than their diagonal, 0.036".

Small drill sizes are numbered, and the number you want is #64 for that exact size, and probably #61 or 1mm (0.03937") would work as well. Recommended drill speeds for such a drill are high, 30000 rpm or so PCB drill , and carbide tooling is recommended if you want long drill life. That's why a 'hardware store' might not have the drill bit you want. Dremel makes suitable drills, and industrial suppliers stock suitable drill bits.


It is really an annoying situation when you can not find the tools you want. How ever, as a solution, I would recommend you to drill using the 1/32 inch drill bit and then use a needle file or 1mm file to adjust the diameter of the hole.


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