I created an Eagle part that has several holes to solder 0.1" pitched break away male headers to, such as the one below.

However the pad has a hole thats too narrow for the header! What drill size should be used? I used the default of 0.03149606

• What does the vendor say? – Ignacio Vazquez-Abrams Dec 7 '14 at 1:55
• @IgnacioVazquez-Abrams I can find the pitch and mating post length, but not the diameter of the mating post. Is there a standard diameter for these? – Nyxynyx Dec 7 '14 at 1:58
• Did you see the "Recommended Hole Pattern" in the drawing linked to on that page? – Ignacio Vazquez-Abrams Dec 7 '14 at 2:02
• Doesn't Eagle have a bunch of male header parts already in it? – Passerby Dec 7 '14 at 3:07
• @IgnacioVazquez-Abrams Vendor probably says "孔必须足够大，并不能太小" :) – Kamil Dec 7 '14 at 6:19

SparkFun has an Eagle library that has pads for single and dual row 0.1" headers from 1 to 40 pins. Here is one of several 1x03 headers (single row, three pins):

The holes have a 40 mil diameter. The yellow square posts, which are for reference only, are drawn with 20 mil sides instead of the standard 25 mils, but expanding the sides out to 25 mils and then measuring the distance from the corners to the edge of the hole shows a 3 mil clearance.

Their library SparkFun.lbr can be downloaded here. It works with both version 5 and version 6 (I haven't tried it on version 7 yet). They also have a set of libraries in the new XML format (version 6 and later) here.

As swebere has pointed out, single and double row headers are also available in some of the libraries whhich are installed with Eagle, such as pinhead. Here is a single row 1x03 header with long pads:

• Why an external library? The buiild-in pinhead.lbr already has single/dual row headers. In addition, it uses long pads, for single row headers, which gives a bit more stability. – sweber Dec 7 '14 at 17:28
• @sweber yep, I've used those too, I just happen to like the SparkFun versions. But good to point out. – tcrosley Dec 7 '14 at 17:35
• @sweber What are long pads? – Nyxynyx Dec 7 '14 at 17:59
• @Nyxynyx I updated my answer to include the long pad headers. – tcrosley Dec 7 '14 at 18:05

The pins in the common 0.1" post headers are .025" square.

For .025" square posts, I usually specified .040" finished hole size (size after plating). For square posts, the hole must be slightly larger than the diagonal measurement of the post.

• Ditto. For 20+ years, my default hole size for 0.1" spacing headers has been 0.040 if I have to make the hole manually. – lyndon Dec 7 '14 at 22:01

Did this up graphically for ref, and for 50-mil calcs. Using the .040" hole for the .025" yields a radial-clearance of ~.0023", see below.

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Note the dimensions are x10 here, makes for a clearer picture to illustrate.

If interested, this yields a 0.0273" hole for a 50-mil header, a 0.7mm drill seems best here.