Manual says to use drill bits as gauge but numbers?

69_340_GTS said

You'll notice that most of the number/letter sizes are perfect to use as drills for various sizes of taps. If you work in the machining field these things become etched into your memory.

Most of this "crap" can be blamed on the British. For example the number drill sizes are based on the British "Stubs Steel Wire Gauge" from the 1800s.

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^^^this^^^buy a tap and bit set and you'll get a #25 bit for a 10-24 tap now go to your local tool store and try and replace the #25 .

PS you will notice that neither chart gives you an actual size that you can walk in and ask for as a replacement #25 but that 10-24 tap is one that I use a thousand times a year doing door hardware .