Drill Bit Sizing

[Jim McDonald]

This may have been covered here previously, but I couldn't find it doing a search of this section.

Many instructions list drill bit sizes as a two digit number, while some list the fractional (inch) measurement. [Must be crazy for those enlightened folks who adopted metric and stuck with it ].

Is there a chart somewhere showing the bit size # as it translates to inch fractional values?

A big thanks to all who have taken the time to answer what might seem like simple, yet repeatitive questions.

[Plaquerd]

Jim
Check out this link.
Drill Bit Chart

It should help you. This is also a great association to belong to. Hope it's what you are looking for.

[GrayBeard Phil]

Jim,

Sit a spell, and let me tell you a story, well some might even go so far as call it a rumor. Have a smoke if you like, I won't mind a bit.

See, first there was the fraction drills and everybody understood that. But that Henry Ford guy and those Automobile folks had a problem with bolts and screws. Seems that you need a slightly smaller drill bit for a hole you are going to make treads in, they call it Tapping the threads. These slightly smaller than the fraction drill bits the auto industry called letters of the Alphabet: A, B, C, D, and so on.

Of course, they latter discovered that depth of the threads you cut in metal depended on the type of metal, the metal of the bolt, and how tight you wanted to make the bolt, and they made charts. All kinds of charts.

So, now industry had fraction and letter drills.

But when Vacuum Tube radios and a bit later WW-II, they needed smaller screws threaded into chassis. But they already used up the letter A for tapping threads for a 1/4 inch machine screw. So some really smart people decided to start using numbers. The next needed size was called a #1, and as smaller sized drill bits were needed, a larger sized number was assigned. Thus, the wise men hoped, they won't run out again.

Now, as they started to standardize these smaller machine screws, some folks noted that some of these new machine screws were, by eyeball, about the size of a 8 penny nail, some were sized about like a 6 penny nail and dang if some weren't about like a 4 penny finishing nail. And they called them #8, #6, or #4 machine screws after a while.

But to drill a hole in some metal, that you would later going to tap, well, you needed to know the correct number of the drill bit. Again, lots of charts and more charts for type of metal, clearance holes, tapping holes, type of head on the bolt, or screw, and so on. Did I mention lots of charts?

-I haven't lost you yet I hope, there is more to come. Did you need some Iced Tea? Anyway back to my tale....

So at about this time in my story, about the smallest any one in industry needed was a #60 drill. Now that drill is real small, (in it's day you understand.) That's about the size hole you needed to drill for tapping the threads for that tiny screw in your eyeglasses. You know, that tiny screw that you can never find the right size screwdriver for when you know you have 3 or 4 somewhere in the house. Right, the one you know the wife has 'm stashed somewhere, and you ain't going to ask!

Then the electronics and computer people needed smaller drills for all their tiny components, mounted on a printed circuit board. So now, the drill sizes go down to #80.

but a strange thing happened on the way to getting smaller and smaller drill bits. A whole lot of the electronics industry manufacturing started to move to countries where the standard is metric. So about now in this story, as smaller and smaller drill bits are being made, they all are metric sized like a 1mm or 0.1 mm. These drill bits are used by automatic machine tools of course. And the electronic part is inserted into the hole by automatic machines also.

Well that's my story, got most of that from my Grandfather. I embellished a bit in the end. He started out on a farm, worked in a repair shop for Railroad engines, and ended up making factory jigs and fixtures for a big automaker before he retired.

Yes, he's the same one that told me that when he was a young man, just before my father was born, he worked a short time in a place that applied a finish to wood furniture. The place got hold of some whiskey that had gone bad aging in the barrel and couldn't be sold for drinking, so the whiskey maker sold it to woodworking shops to be mix with Shellac. He claimed that this whiskey shellac was highly prized by the senior men in that shop. Used only for prized customers. Something about the amber color from the charred inside of the aging whiskey barrel.

Well, I hope you enjoyed my long winded tale.

Phil

[greatdane2]

So to sum it all up, you are saying too many IDIOTS had a finger in the pie.

[Fremmed]

Ok, I got the stuff about the whiskey shellac. Now could you explain the part about the drill bits again?LOL

[Dragon]

I need a nap!
Diane

[Rolf]

If you think drill bits are fun try working on old Brit mechanicals. ( One of my favorite hobbies) I have Inch ,Metric and Witworth wrenches.(oops Spanners)

[Wood Dog]

Wow the knowledge one can learn from this forum is phenomenal........factual, or yarn it was a fun read.

[Ramjet]

When I was pulling wrenches years ago , one of the welders approached me with a puzzled look on his face , He couldn't understand why his wrenches wouldn't fit the heads of the bolts . It was in the late 1970's when vehicles were switching over to metric , at least here in Canada .. The truck was built using a combination of metric and standard . He wasn't about to purchase a whole new set of metric wrenches . Most shops started providing them . Roger

[RollaJohn]

Here is a web site that has a listing of the number, fractional, letter and metric sizes and their decimal inch equivalents in ascending order. The sizes range from 0.0098 inch (0.25 mm) up to 1.000 inches.

Drill Size Conversion Table

I like this style, as opposed to the ones like on the SAW site, because it is easy to go to the next size larger or smaller available drill without having to check each of the different chart listings and having to compare.

I refer to both of these and wish I could locate one all inclusive table that would give all the bits in ascending order that are available. Neither table gives all the sizes available, but by using both most of the bit sizes are shown.


Phil, thanks for the history lesson on how the sizes came to be. Very interesting.



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