View Full Version : Need a #7 Drill Bit for 1/4-20NC Tap. What is a #7?


keithdigital
09-15-2011, 06:16 PM
I need to use a 1/4-20NC tap. The Tap Drill selector says to use a #7 Drill Bit. What is a #7 Drill Bit and where do I buy one?

Thanks!

Steevo
09-15-2011, 06:21 PM
There are three standard sets of drill bits. Fractional, Number and Letter
A typical Number (or "wire gauge" ) bit set is numbered from 1 to 60.

#7 is just barely smaller than 13/64", but quite a bit bigger than 3/16"

Here is a good chart:
http://www.custompartnet.com/images/size-charts/drill-size-chart-english.png

bczygan
09-15-2011, 06:27 PM
Here is a link to a chart:
http://www.csgnetwork.com/drillsizeconvert.html

If you don't have a number 7, notice that 13/64 is just 2 thousandths bigger.

Jim Johnstone
09-15-2011, 06:30 PM
#7 is a 0.201" diameter bit, 13/64" is 0.203" diameter.

keithdigital
09-15-2011, 07:04 PM
Ok so there will be enough threads to grab if I use a 13/16"?

And where would you purchase Wire Gauge Drill Bits - I called up Home Depot and they didn't know what I was talking about.... ??

Jim Johnstone
09-15-2011, 07:17 PM
13/64" is more than close enough to work with 1/4-20 tap. #'d drill bits should be easily available from any decent industrial supply house.

kf4zht
09-15-2011, 07:19 PM
Ok so there will be enough threads to grab if I use a 13/16"?

And where would you purchase Wire Gauge Drill Bits - I called up Home Depot and they didn't know what I was talking about.... ??

They may have one, but it will be packaged with a tap in a kit.

I would recommend looking at other suppliers for machining tools. Enco, real hardware shops, MSC, Grainger, Harry Epstein, Fastenall, the list goes on.

If you have the money I would pick up a US made 115 pc drill set. It will include Fractional up to 1/2", 0-60 and A-Z. With some occasional sharpening and care it will last a lifetime.

Milton Shaw
09-15-2011, 07:20 PM
Northern tool sells a set, i think its 115 bits that are number, letter and fractional bits. Not a lot of money and not the best, but it has the sizes. Home Depot and Lowes, would not have any idea of what you are talking about. MSCDirect and Enco both have these drill sets in various grades. Also they have the Silver and Demming type bits in several grades. (large diameter 1/2" shank)

oldwino
09-15-2011, 10:09 PM
I've found the local ACE hardware has number drills...probably better than buying a complete set if you only need one

Gtamazing
09-15-2011, 10:43 PM
#7 is a 0.201" diameter bit, 13/64" is 0.203" diameter.

This^^^

unless your making airplane parts.

Outlawmws
09-15-2011, 11:30 PM
Any decent hardware store will sell drills in sets and individually. The big box Home Improvements may not sell them individually.

Griff93
09-16-2011, 12:06 AM
Ok so there will be enough threads to grab if I use a 13/16"?

And where would you purchase Wire Gauge Drill Bits - I called up Home Depot and they didn't know what I was talking about.... ??

I'm assuming this is a typo. If not, do not ask for a 13/16. It will be way to large. A 13/64 is way smaller than a 13/16.

Here's a #7 bit from enco. I'd recommend as others have of buying the 115 piece set if you have the money. I bought the USA one from enco and have used it for years. They still work well and I'm very happy with them. Enco also has some nice tap handles as well if you are going to be doing this a lot. Drill bushings can be used as tapping blocks to start the tap relatively square to the hole.
http://www.use-enco.com/CGI/INSRIT?PMAKA=317-7484&PMPXNO=19500892&PARTPG=INLMK32

Brad54
09-16-2011, 12:49 AM
I'll pile on the "Buy a full set" bandwagon.

Just a couple weeks ago, a special fastener busted on the Corvair: It's a clutch cable pulley bolt: it had a 1/2-inch shoulder, with a 1/4-20 stud coming off it. Slip it through the pulley, into the bracket, put a nut on the 1/4-20 "stud."
The stud snapped off.
I was able to grind the busted part off, flush to the shoulder, drill the end of the shoulder with the exact correct size bit, tap it with a 1/4-20 tap, then use a bolt in place of the original stud/nut arrangement. When I was done, it not only looked factory, but it was only a hiccup in the day's activities, rather than a project ender until I could order this special hardware from Clark's Corvair and wait for it to be delivered.

THAT'S what having a shop full of tools is all about!

-Brad

keithdigital
09-16-2011, 07:07 AM
I'm assuming this is a typo. If not, do not ask for a 13/16. It will be way to large. A 13/64 is way smaller than a 13/16.


Yes I meant 13/64, Thanks!

Great advice guys, and I now understand Numbered and Lettered Drill Bits. I will definitely consider the 115 piece set.

woody 73
09-16-2011, 07:15 AM
I sent you a pm with a company phone number if you just want to buy the #7 bit.

keithdigital
09-16-2011, 09:50 PM
I sent you a pm with a company phone number if you just want to buy the #7 bit.

Thanks Woody!