History of drill sizes

While at the "Big Box with Nothing WE Need" store, looking at their available bolts, the list of taps we had, tapping charts, and drills they did have; we started wondering..

What's the history behind the letter and number drill sizes?

Reply to
David Lesher
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Don't know about the letters, but the fact that the number drills are sometimes called "wire gauge" might be a clue. Which one of the many wire gauges existing back in the 1800s would be the question. If you wonder about the machine screw numbering system, look up "Sellers system".

Stan

Reply to
stans4

You might also not that even though everything they have uses metric screws/bolts, there is not a single metric drill bit or tap/die that is metric.

Paul

Reply to
KD7HB

"Big Box with Nothing WE Need" store, looking at

Lancashire wire gauge for the lettered sizes:

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Reply to
Denis G.

Google "history of drill bit sizes" the next time you have nothing else to do. The subject has apparently come up on several forums from time to time and there is plenty to read on the issue.

My own take on all this (relating to the fractional and number/letter sizes that most of us in the US use)is:

They (whoever "they" is) started out with coarse fractions when they didn't need anything very accurate. Let's say fractions of an inch, by

1/16ths. As precision needs increased, they got down to 32nds and then 64ths. I'm guessing that, at least in "them thar days", the highest degree of precision was needed in the smaller sizes, so: when, they needed even more precision, here come the letters and numbers to fill in the gaps between the 64ths. One of the posts that I did follow suggests that the numbers follow the "Stubbs" wire gage very closely and that, since the bits were often made from drawn wire, that's where the numbers came from. Take a look at that suggested Google search and draw your own conclusions. One last comment (this has been addressed here in the past, too, I'm sure: In the rare case where I need a drill bit size that isn't in the fraction/number/letter set, I go for a metric equivalents.

Pete Stanaitis

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David Lesher wrote:

Reply to
spaco

Along those lines, I operated a lathe, which must have dated from the

1860's, that had the cross feed dial calibrated in 1/28th inch. It was (from memory) about a 12 X 48" machine and had been converted from overhead shaft to electric motor power.
Reply to
john B.

Explain letter "E" at 0.2500"

The guy that made the letter drills was tired of his 1/4" drill missing from the set so he duplicated it. (my guess)

Reply to
Randy333

e = 2.718281828459045, not 2.5000

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Reply to
Josepi

The charts for lettered wire gauges are about 1/2-way down the page:

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Reply to
Denis G.

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