What are lettered drill bits

[BOB OLINGER]

Maybe I'm living in the dark, but I know you guys can lighten me up. I'm making plantation shutters and the need is for the proper sized drill bits for the shutter pins. I have a set of brad point bits in 64ths, but still not quite right. On Norm's plan, he suggest a size "B" bit. I'm not familiar with letter or numbered size bits. Can someone enlighten me? Also, where can I but just 1 or 2 bits without buying a whole set? Thanks, a lot.

[Rod Sheridan]

Hi Bob, the other common imperial drill sets are numbers and letters, which are drills that are in non fractional sizes.

Any industrial supply shop will have number and letter bits available for individual purchase.

Regards, Rod.

[Bob Eddy]

Look here: http://www.csgnetwork.com/drillsizeconvert.html#

[John Downey]

Size b is 0.2380"

Letter sizes are just the larger version of the numbered wire sizes, often used for tapping (so you don't have to remember the size in inches). Places that sell machining supplies will stock them (like McMaster Carr, Enco, MSC, Victor Machinery - I buy bandsaw blade stock from them). There used to be a couple local machine tooling suppliers in every city it seemed like, but with so much going mail/internet, and so many smaller machine shops closing up, can't count on that any more.

Here's a conversion chart for drill sizes.
http://www.csgnetwork.com/drillsizeconvert.html

[Joe Mindell]

I know that the numbered bits correspond to 'wire gauges.' these are the standard sizes that wire comes in. Larger numbers represent smaller wires. There's a lot of subtle gradations here between 12 and 14 gauge (which are household electrical wires), gauges in the 20's, which are in small electrical appliances, and even smaller ones (I seen bits as small as #60).

I've only used these in an amateur way, so I don't know the details, but I know that sometimes one of these works where a standard fractional size doesn't.

[george wilson]

There are fractional drills,numbered drills,letter drills,and metric drills. Each type gives you sizes in between what fractional drills offer. For much of my career,I got along fine with just fractional drills and number drills. Then I got a set of letter drills,and finally some metric drills.

Number drills give you a much better selection in the smaller sizes,and go down to # 80, ABOUT .0135". The letter drills are drills in larger sizes from ABOUT 1/4" to ABOUT 1/2" range. I use them seldom,so can't recall the exact beginning and ending sizes. A 1/4-20 thread uses an "F" size drill,but you aren't going to die if you use a close fractional drill substitute. Taps are only supposed to produce a 75% thread,anyway. If you use a drill that is just a wee bit too small,you are liable to break the tap.

I'm speaking in vague terms for the beginner to understand.

Do you guys know what brass drills are like?

[Horton Brasses]

Do you guys know what brass drills are like?

Do you mean an actual brass bit or drilling through brass?

Brass is very soft and tears easily if you are drilling. Not sure if that's what you mean or not. Use a HS steel bit at a high RPM and drill slowly-from the back to get a cleaner hole. Punch the hole if you can. We punch holes wherever possible.

[BOB OLINGER]

Thanks for all the answers and then some. I can't believe I've not stumbled onto this before. Anyway, the local machine shop has them in inventory; also, the Woodsmith Store but that's 40 mi. away.

[Paul Ryan]

Bob,

As George aluded to ealier don't go out of your way to find exactly the same size. I have tapped thousands of things in metal that asked for a letter or number size and I used a fractional or metric size. If you are dealing with wood a 1/4 bit is a little smaller than the B but should be just fine. Otherwise a 6mm bit is only .0018 too small. No enough of a difference to make any difference especially in wood.

[mickey cassiba]

The letter size bits are there to confusticate you!!! Just Kidding! As I was told, years ago, there was a need for drill sizes between the fractional sizes. The numbered sizes corresponded to wire/sheet metal gages, but above No.1 there wasn't any way to name the larger sizes.Thus the letter gages. Might be an old wives tale, but she sure was a hairy, ugly old wife!

[Cliff Rohrabacher]

One fellow explained to me why they originated with letter designations.
I forget what he said.

I'd prefer to have drills in the inch standard divided up on the decimal system.

Fractions are a royal PITA so too the letters and numbers. I used to have all of the decimal equivalents memorized.
One of the advantages to the metric system that they all work off base 10.

But, I refuse to get any metric measuring tools because it is a proven fact that metrics are inherently dangerous.

[Jerry Bruette]

There are fractional drills,numbered drills,letter drills,and metric drills. Each type gives you sizes in between what fractional drills offer. For much of my career,I got along fine with just fractional drills and number drills. Then I got a set of letter drills,and finally some metric drills.

Number drills give you a much better selection in the smaller sizes,and go down to # 80, ABOUT .0135". The letter drills are drills in larger sizes from ABOUT 1/4" to ABOUT 1/2" range. I use them seldom,so can't recall the exact beginning and ending sizes. A 1/4-20 thread uses an "F" size drill,but you aren't going to die if you use a close fractional drill substitute. Taps are only supposed to produce a 75% thread,anyway. If you use a drill that is just a wee bit too small,you are liable to break the tap.

I'm speaking in vague terms for the beginner to understand.

Do you guys know what brass drills are like?

I don't mean to be picky, George, but a 1/4-20 tap requires a #7 drill bit and a 5/16-18 tap requires a letter size F drill.:)

Jerry

[BOB OLINGER]

I picked up a size "B" at our local machine supply on the way home last night for $3.61. I bored out the holes previously at 15/64". The result was the shutters move beautifully. Hard to imagine that .0036" would make a difference but I guarantee you it did on this work. So, thanks again for the answers, input, and comments.