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Drill bit sizes

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Terry Pinnell

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Apr 22, 2013, 12:01:07 PM4/22/13
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I've just been drilling a few holes in brick for a fixture specifying a
size 7 mm masonry drill bit. I found one in my collection marked '7' but
as I thought it looked a bit small I measured it with my micrometer. To my
surprise the shank diameter was only 5.1 mm. Measuring the drilling
section itself was slightly tricky but that too seemed similar.

Am I missing something here, or is the bit just likely to have been
engraved incorrectly?

Also, can anyone recommend a simple tool to measure standard drill bits in
the popular sizes please. Presumably it would simply be a strip of
thickish plastic, drilled with a set of clearly marked holes. Even better
if it also has holes for the correct matching rawlplug.

--
Terry, East Grinstead, UK

Jules Richardson

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Apr 22, 2013, 12:07:32 PM4/22/13
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On Mon, 22 Apr 2013 17:01:07 +0100, Terry Pinnell wrote:

> I've just been drilling a few holes in brick for a fixture specifying a
> size 7 mm masonry drill bit. I found one in my collection marked '7' but
> as I thought it looked a bit small I measured it with my micrometer. To
> my surprise the shank diameter was only 5.1 mm. Measuring the drilling
> section itself was slightly tricky but that too seemed similar.

7/32" maybe? That would work out as 5.5mm, I think.

cheers

Jules

harry

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Apr 22, 2013, 12:16:23 PM4/22/13
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The tungsten carbide tip on a masonry drill is significantly bigger
than the shank.

Also, they get smaller with use, the sides wear as well as the
"front". (So drilling ever smaller holes.)

Nightjar

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Apr 22, 2013, 12:20:23 PM4/22/13
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On 22/04/2013 17:01, Terry Pinnell wrote:
> I've just been drilling a few holes in brick for a fixture specifying a
> size 7 mm masonry drill bit. I found one in my collection marked '7' but
> as I thought it looked a bit small I measured it with my micrometer. To my
> surprise the shank diameter was only 5.1 mm. Measuring the drilling
> section itself was slightly tricky but that too seemed similar.
>
> Am I missing something here, or is the bit just likely to have been
> engraved incorrectly?...

It is a number 7 drill, which has a diameter of 5.1mm.

For a full list of number and letter drill sizes:

http://shopswarf.orconhosting.net.nz/drills.html

Colin Bignell

charles

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Apr 22, 2013, 12:21:51 PM4/22/13
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In article <human8pjtdrfdg6ul...@4ax.com>,
Terry Pinnell <terry...@DELETEgmail.com> wrote:
> I've just been drilling a few holes in brick for a fixture specifying a
> size 7 mm masonry drill bit. I found one in my collection marked '7' but
> as I thought it looked a bit small I measured it with my micrometer. To my
> surprise the shank diameter was only 5.1 mm. Measuring the drilling
> section itself was slightly tricky but that too seemed similar.

> Am I missing something here, or is the bit just likely to have been
> engraved incorrectly?

on all my small masonry drills, the shank is smaller than the head. I've
just measured a 7mm SDS drill and teh shank is 6.1mm.
The head on yours might have worn away

--
From KT24

Using a RISC OS computer running v5.18

Dave Plowman (News)

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Apr 22, 2013, 12:53:59 PM4/22/13
to
In article <human8pjtdrfdg6ul...@4ax.com>,
Terry Pinnell <terry...@DELETEgmail.com> wrote:
> I've just been drilling a few holes in brick for a fixture specifying a
> size 7 mm masonry drill bit. I found one in my collection marked '7' but
> as I thought it looked a bit small I measured it with my micrometer. To
> my surprise the shank diameter was only 5.1 mm. Measuring the drilling
> section itself was slightly tricky but that too seemed similar.

Older drills were marked using the number system - like No 8 woodscrews,
etc. Modern ones are likely to be marked with a number which is mm. But
the two ain't the same.

--
*Some people are only alive because it is illegal to kill.

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.

meow...@care2.com

unread,
Apr 22, 2013, 3:08:56 PM4/22/13
to
On Monday, April 22, 2013 5:01:07 PM UTC+1, Terry Pinnell wrote:

> Also, can anyone recommend a simple tool to measure standard drill bits in
> the popular sizes please. Presumably it would simply be a strip of
> thickish plastic, drilled with a set of clearly marked holes. Even better
> if it also has holes for the correct matching rawlplug.

Drill bit gauge IIRC. Use gently if plastic. Very useful timesaver.


NT

Terry Pinnell

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Apr 23, 2013, 2:50:27 AM4/23/13
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Thanks all, much appreciated. Hadn't realised bits used a numbering system
like wire guages.

The markings wear off quickly so a guage seems the best approach. Googling
'drill bit gauge' found 'Silverline Drill Gauge (1 - 13mm', which looks
what I'm after. And maybe its imperial equivalent (1/16" - 1/2").

Terry Pinnell

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Apr 23, 2013, 2:58:07 AM4/23/13
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... although the 1 - 13mm item appears to be marked in imperial
measurements!
http://www.tikproducts.co.uk/silverline-drill-gauge-1-13mm?language=en&currency=GBP

Nightjar

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Apr 23, 2013, 3:41:11 AM4/23/13
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On 23/04/2013 07:50, Terry Pinnell wrote:
...
> Thanks all, much appreciated. Hadn't realised bits used a numbering system
> like wire guages.
...

It is an old system and I don't recall when I last used it to order
drills larger than about 1mm dia.

Colin Bignell

Dave Plowman (News)

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Apr 23, 2013, 5:37:00 AM4/23/13
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In article <Sd-dnbHA7eKEpuvM...@giganews.com>,
The number system sometimes used for masonry drills isn't the same as for
'normal' HSS drills, though.

I've dug out some old masonry drills - not much used since I got an SDS -
and one at random is marked 6.5 1/4 No12. It would date from the days of
fibre Rawlplugs where you used the same number for drill, plug and screw.

--
*I wonder how much deeper the ocean would be without sponges*

Terry Pinnell

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Apr 23, 2013, 8:38:55 AM4/23/13
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"Dave Plowman (News)" <da...@davenoise.co.uk> wrote:

>In article <Sd-dnbHA7eKEpuvM...@giganews.com>,
> Nightjar <c...@insert.my.surname.here.me.uk> wrote:
>> On 23/04/2013 07:50, Terry Pinnell wrote:
>> ...
>> > Thanks all, much appreciated. Hadn't realised bits used a numbering
>> > system like wire guages.
>> ...
>
>> It is an old system and I don't recall when I last used it to order
>> drills larger than about 1mm dia.
>
>The number system sometimes used for masonry drills isn't the same as for
>'normal' HSS drills, though.
>
>I've dug out some old masonry drills - not much used since I got an SDS -
>and one at random is marked 6.5 1/4 No12. It would date from the days of
>fibre Rawlplugs where you used the same number for drill, plug and screw.

I wish that was still the case as I usually find matching all three no
simple task!

Nightjar

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Apr 23, 2013, 8:49:21 AM4/23/13
to
On 23/04/2013 10:37, Dave Plowman (News) wrote:
> In article <Sd-dnbHA7eKEpuvM...@giganews.com>,
> Nightjar <c...@insert.my.surname.here.me.uk> wrote:
>> On 23/04/2013 07:50, Terry Pinnell wrote:
>> ...
>>> Thanks all, much appreciated. Hadn't realised bits used a numbering
>>> system like wire guages.
>> ...
>
>> It is an old system and I don't recall when I last used it to order
>> drills larger than about 1mm dia.
>
> The number system sometimes used for masonry drills isn't the same as for
> 'normal' HSS drills, though.
>
> I've dug out some old masonry drills - not much used since I got an SDS -
> and one at random is marked 6.5 1/4 No12. It would date from the days of
> fibre Rawlplugs where you used the same number for drill, plug and screw.

I think the drill number system is the same, apart from, as you note,
those sold by Rawlplug for use with their wall plugs.

Colin Bignell

Andrew Mawson

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Apr 23, 2013, 9:19:07 AM4/23/13
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"Terry Pinnell" wrote in message
news:050dn8h85c7vj4gk1...@4ax.com...
The plastic plugs that come all moulded in one chunk say on them the range
of screw sizes they cover and the size of drill required. Vast majority of
applications are covered by the Red plugs that need a 6 mm hole, and the
Brown ones that need a 7 mm hole. I try to standardise on the Brown ones
which will take a number 7 to a number 12 screw.

AWEM


Dave Plowman (News)

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Apr 23, 2013, 10:12:45 AM4/23/13
to
In article <050dn8h85c7vj4gk1...@4ax.com>,
Terry Pinnell <terry...@DELETEgmail.com> wrote:
> >I've dug out some old masonry drills - not much used since I got an SDS
> >- and one at random is marked 6.5 1/4 No12. It would date from the days
> >of fibre Rawlplugs where you used the same number for drill, plug and
> >screw.

> I wish that was still the case as I usually find matching all three no
> simple task!

Plastic plugs are usually stated to take a variety of screw sizes with
just the one drill - so should be easier. Better makes say the drill size
on the strip they're attached to - or even have a hole to check the drill
with.

--
*Do paediatricians play miniature golf on Wednesdays?

Scott M

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Apr 23, 2013, 3:59:35 PM4/23/13
to
Andrew Mawson wrote:

> The plastic plugs that come all moulded in one chunk say on them the
> range of screw sizes they cover and the size of drill required. Vast
> majority of applications are covered by the Red plugs that need a 6 mm
> hole, and the Brown ones that need a 7 mm hole. I try to standardise on
> the Brown ones which will take a number 7 to a number 12 screw.

IMO, brown plugs are way too big for #7 or #8 screws.

I use:

Yellow, 5mm/5.5mm hole (depends on make of plug) for #6/#8
Red, 6mm for #10
Brown, 7mm for anything larger and coach screws & the like.

Scott

Terry Pinnell

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Apr 24, 2013, 3:04:44 AM4/24/13
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In practice I frequently end up using trial/error. A major factor is the
material. Holes in breeze block and soft wood are always larger than the
drill diameter.

And a frequent problem I have is judging whether the plug will fit. It
either gets stuck irretrievably because it's too large, or has to be
tediously removed after it turns out to be too small.

Also, as the hole, plug and screw respectively become larger as I proceed
towards a solution, the hole in the fixture then sometimes needs enlarging
too!

Andy Champ

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Apr 24, 2013, 4:57:50 AM4/24/13
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On 24/04/2013 08:04, Terry Pinnell wrote:
> And a frequent problem I have is judging whether the plug will fit. It
> either gets stuck irretrievably because it's too large, or has to be
> tediously removed after it turns out to be too small.

To remove a too-small plug - get a long thin screw, and hand-screw it a
turn or too into the end of the plug. Then pull. If it won't come out it
isn't too small :)

Andy

Terry Pinnell

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Apr 24, 2013, 6:18:56 AM4/24/13
to
Yes, thanks Andy, that's my usual method too. But it would be good to have
a reliable, universal procedure that resulted in getting it right first
time ;-)

I reckon the following seems logical and I'll try it next time:

1. Drill the hole (following guidance if there is any).

2. Use a hand vacuum to suck out the remaining dust.

3. Measure the actual diameter by inserting known drill bits until one
fits snugly.

4. Use a plug whose widest diameter (apart from any 'lip' at the end)
matches the hole. I have a micrometer, so should be able to measure that.

5. Use a screw whose widest diameter is X mm smaller than the hole. But
what should be the value of X? And would this vary with the type of plug?

6. Try it - and if I can't tighten it beyond about the 80% depth, replace
with a screw of smaller diameter.

Andy Champ

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Apr 24, 2013, 6:39:08 AM4/24/13
to
On 24/04/2013 11:18, Terry Pinnell wrote:
> Yes, thanks Andy, that's my usual method too. But it would be good to have
> a reliable, universal procedure that resulted in getting it right first
> time;-)
>
> I reckon the following seems logical and I'll try it next time:
>
> 1. Drill the hole (following guidance if there is any).
>
> 2. Use a hand vacuum to suck out the remaining dust.
>
> 3. Measure the actual diameter by inserting known drill bits until one
> fits snugly.
>
> 4. Use a plug whose widest diameter (apart from any 'lip' at the end)
> matches the hole. I have a micrometer, so should be able to measure that.
>
> 5. Use a screw whose widest diameter is X mm smaller than the hole. But
> what should be the value of X? And would this vary with the type of plug?
>
> 6. Try it - and if I can't tighten it beyond about the 80% depth, replace
> with a screw of smaller diameter.

My usual method is to get the drill bit that I know matches (No 8?),
drill a hole, stick a red plug in it, then put a no. 8 screw in. No
vacuuming, no testing. Only thinking is what length of screw.

I only have 3 sizes(1) of masonry bit, so it isn't hard to remember
which one.

Andy
--
(1) well, I also have a half-inch bit for putting cables in.

Rick Hughes

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May 2, 2013, 8:35:46 AM5/2/13
to
On 22/04/2013 17:01, Terry Pinnell wrote:
More than likely a No.7 drill diam seems about right.


Letter and Number drills are as far as I know an old UK anomaly, not
used much nowadays .... listed nicely in my 35 yr old Zeuss book (now
that has been a value for money purchase)

Rick Hughes

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May 2, 2013, 8:37:43 AM5/2/13
to
I have a precision one ... steel plate with brass inserts for each hole
- accurately drilled for drills 1/64" to 1/2"

If I were making one, I'd get a piece of 1/4" thick perspex or similar
and drill the holes.

dochol...@gmail.com

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May 2, 2013, 10:05:03 AM5/2/13
to
On Thursday, May 2, 2013 1:35:46 PM UTC+1, Rick Hughes wrote:
<snip>
>
> More than likely a No.7 drill diam seems about right.
>
>
> Letter and Number drills are as far as I know an old UK anomaly, not
> used much nowadays .... listed nicely in my 35 yr old Zeuss book (now
> that has been a value for money purchase)

Both UK and US - probably more common in US these days than in UK.

Matty F

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May 3, 2013, 6:25:28 AM5/3/13
to
On Tuesday, April 23, 2013 4:01:07 AM UTC+12, Terry Pinnell wrote:

> Also, can anyone recommend a simple tool to measure standard drill bits in
>
> the popular sizes please.

I made a gauge that's basically a long triangular slot in a piece of sheet steel.
Slide the unknown drill down the slot until it stops, and read the imperial size on the left or metric on the right. I also put some yellow paint on all the metric drills.

Alexander Lamaison

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May 3, 2013, 7:00:38 AM5/3/13
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You should patent that idea. It's a goodun.

I don't know how well any gauges work for masonry bits, though. The
size of the hole seems to vary wildly depending on age of bit,
manufacturer, density of material being drilled and pressure applied.

I may be imagining it but high quality bits (DeWalt) seem to make a more
precise hole than cheapos (ScrewFix Titan, Wilko, PP). Odd, because
I've heard people say masonry bits are one type where you can afford to
skimp on quality.

Alex

--
Swish - Easy SFTP for Windows Explorer (http://www.swish-sftp.org)

Matty F

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May 3, 2013, 5:28:28 PM5/3/13
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On Friday, May 3, 2013 11:00:38 PM UTC+12, alamaison wrote:
> Matty F <matty...@yahoo.co.nz> writes:
>
>
>
> > On Tuesday, April 23, 2013 4:01:07 AM UTC+12, Terry Pinnell wrote:
>
> >
>
> >> Also, can anyone recommend a simple tool to measure standard drill bits in
>
> >>
>
> >> the popular sizes please.
>
> >
>
> > I made a gauge that's basically a long triangular slot in a piece of
>
> > sheet steel.
>
> > Slide the unknown drill down the slot until it stops, and read the
>
> > imperial size on the left or metric on the right. I also put some
>
> > yellow paint on all the metric drills.
>
>
>
> You should patent that idea. It's a goodun.

Thanks. I found a picture of my gauge:
http:/i43.tinypic.com/18kirp.jpg

polygonum

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May 3, 2013, 5:40:01 PM5/3/13
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Matty F

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May 3, 2013, 9:12:13 PM5/3/13
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Does anyone make one with Imperial and Metric on the same gauge?
Our workshop uses both, since we repair very old vehicles from anywhere in the world, e.g. an 1869 fire engine.

Clive George

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May 3, 2013, 9:29:29 PM5/3/13
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That axmister one is double sided.

polygonum

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May 4, 2013, 3:38:40 AM5/4/13
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Yes - as Clive said.

"Imperial and metric graduations" - which are found by flipping it over.

--
Rod

meow...@care2.com

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May 4, 2013, 4:57:42 AM5/4/13
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On Saturday, May 4, 2013 2:12:13 AM UTC+1, Matty F wrote:
> On Saturday, May 4, 2013 9:40:01 AM UTC+12, polygonum wrote:
> > On 03/05/2013 22:28, Matty F wrote:

> > > Thanks. I found a picture of my gauge:
> > > > http:/i43.tinypic.com/18kirp.jpg

> Does anyone make one with Imperial and Metric on the same gauge?
> Our workshop uses both, since we repair very old vehicles from anywhere in the world, e.g. an 1869 fire engine.

You could have 4 scales on a slot type, or 8 if the metal's wider, but isnt it easier to just use metric and have a lookup table? I tend to treat all my bits as if they were metric. Perhaps I should rephrase that.


NT

Matty F

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May 4, 2013, 7:56:19 AM5/4/13
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On Saturday, May 4, 2013 8:57:42 PM UTC+12, meow...@care2.com wrote:

> You could have 4 scales on a slot type, or 8 if the metal's wider, but isnt it easier to just use metric and have a lookup table? I tend to treat all my bits as if they were metric. Perhaps I should rephrase that.

I would find it much slower to look at a table than to simply read off say 13/64ths and put the drill away. I seem to need to sort out a hundred drills quite often when people misfile them.
Same with bolts. I have made a slot gauge for bolts from 1/16th to 1.25" and have a single table in ascending diameter for metric, Whitworth, unified, and BA, since we use all of those.

meow...@care2.com

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May 5, 2013, 5:12:44 AM5/5/13
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I guess with a long scale you can fit all the markings you want on. Each scale in a different colour should make life easier.


NT
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