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Types of Holes – The Complete Guide
by The Engineer's Bible | Updated: 07-Oct-2022
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This is a complete guide to the types of holes found in machining.
In this guide you’ll learn:
The different types of holes used in machining.
What the difference is between counterbore and countersink holes.
The symbols used for each hole and how they are shown on engineering
drawings.
How each type of hole is used in engineering.
So if you want to learn the different types of holes used in engineering, you’ll love
today’s guide.
Let’s get started.
Table of Contents

1. Simple Hole
1.1. What Is a Simple Hole?
1.2. What Is the Symbol for a Simple Hole?
1.3. How Are Simple Holes Shown on Engineering Drawings?
2. Counterbore
2.1. What Is a Counterbored Hole?
2.2. What Is the Counterbore Symbol?
2.3. How Are Counterbores Shown on Engineering Drawings?
2.4. What Are Counterbored Holes Used For?
3. Spotface
3.1. What Is a Spotface?
3.2. What Is the Spotface Symbol?
3.3. How Are Spotfaces Shown on Drawings?
3.4. What Are Spotfaces Used For?
4. Countersink
4.1. What Is a Countersunk Hole?
4.2. What Is the Countersink Symbol?
4.3. How Are Countersinks Shown on Drawings?
4.4. What Are Countersunk Holes Used For?
5. Counterdrill
5.1. What Is a Counterdrilled Hole?
5.2. What Is the Counterdrill Symbol?
5.3. How Are Counterdrills Shown on Drawings?
6. Taper
6.1. What Is a Tapered Hole?
6.2. What Is the Tapered Hole Symbol?
6.3. How Are Tapered Holes Shown on Drawings?
6.4. What Are Tapered Holes Used For?
7. Screw Clearance
7.1. What Is a Screw Clearance Hole?
7.2. What Is the Screw Clearance Symbol?
7.3. How Are Screw Clearance Holes Shown on Drawings?
7.4. What Size Screw Clearance Hole Should I Use?
7.5. What Are Screw Clearance Holes Used For?
8. Tapped Hole
8.1. What Is a Tapped Hole?
8.2. What Is the Tapped Hole Symbol?
8.3. How Are Tapped Holes Shown on Drawings?
8.4. What Are Tapped Holes Used For?
9. Conclusion
Simple Hole
What Is a Simple Hole?
A simple hole is a circle that has been cut out of an object.
If we cut the block in half, it looks like this:
What Is the Symbol for a Simple Hole?
The symbol used for a hole is the diameter ‘Ø’ symbol.
How Are Simple Holes Shown on Engineering Drawings?
Simple holes are shown on engineering drawings by stating the diameter and the depth
of the hole.
For example, a 20 diameter hole that goes straight through the component would be
represented as “Ø20 Through”.
Holes that go all the way through the component are known as through holes.
Holes that do not go completely through the material are known as blind holes.
Through
Hole
Blind
Hole
Holes can be shown as a section view in order to show a clearer image of the depth of
the holes.
The bottom view is what we would see if we cut the top view in half along the ”A’
section line.
The shape of the bottom of the hole is determined by the tool used to create the hole.
For a drilled hole, the shape of the bottom of the hole will be determined by the drill tip
angle.
If the hole is created by a process called ‘boring’ or by a tool with a zero tip angle, the
bottom of the hole will be at.
These two types of blind hole drilling are shown in the drawing below:
Counterbore
What Is a Counterbored Hole?
A counterbore is a simple hole with a wider hole above it.
The 3D model below shows a counterbore with the same counterbore next to it cut in
half:
What Is the Counterbore Symbol?
The symbol used for a counterbore is ‘⌴’.
How Are Counterbores Shown on Engineering Drawings?
Counterbored holes are shown on engineering drawings as follows:
The top view shows how counterbored holes are shown on drawings. The bottom view
explains what the counterbore dimensions are showing.
Note for counterbored holes that the pilot hole usually goes completely through the
component. That’s why there isn’t a ‘Through’ or a dimension after the pilot hole
diameter, because it is assumed it goes all the way through.
A ‘pilot hole’ is a small diameter hole, usually the rst hole to be drilled.
The counterbore example above was for an M20 socket-head bolt with normal
clearance. You can nd out what size counterbore you need by looking at a chart such
as this one.
What Are Counterbored Holes Used For?
Counterbores are machined for socket-head screws. They are used for applications
where the bolt or screw must sit beneath the surface.
For example, in applications where there isn’t space for a hex-head bolt to be used due
to clearance issues:
A washer may also be present underneath the socket-head screw.
Spotface
What Is a Spotface?
A spotface is a shallow counterbored hole.
What Is the Spotface Symbol?
The symbol for a spotface is the counterbore symbol with the letters ‘SF’ inside it:
How Are Spotfaces Shown on Drawings?
An example of a spotface is shown below, the dimensioning is very similar to a
counterbore.
What Are Spotfaces Used For?
Spotfaces are used for creating a smooth and at surface.
For example, a component that has been made via casting may not have a smooth and
at surface like a machined component.
Therefore a spotface is machined, ensuring that a part to be connected to a component
with a rough surface is located correctly.
Countersink
What Is a Countersunk Hole?
A countersink is a simple hole with a conical hole above it.
The 3D model below shows a countersink with the same countersink next to it cut in
half:
What Is the Countersink Symbol?
The symbol for a countersink is ‘⌵’.
How Are Countersinks Shown on Drawings?
Countersunk holes are shown on drawings as follows – the bottom section view shows
what the top dimension refers to.
If the countersink was a blind hole, the ‘Through’ above would be replaced with the
depth of the pilot hole.
You may be wondering what the ‘Ø40.32′ is. This is known as the theoretical edge and
this size countersink is for an M20 countersunk bolt.
You can nd out the countersunk dimension required for countersunk metric bolts here.
What Are Countersunk Holes Used For?
Countersunk holes are used for applications where a countersunk bolt or screw is
required.
Like counterbore holes, countersink holes ensure the bolt or screw sit below the
surface.
Counterdrill
What Is a Counterdrilled Hole?
A counterdrilled hole is like a countersunk hole but there is a recess above it.
The 3D model below shows a counterdrilled hole with the same counterdrilled hole next
to it cut in half:
What Is the Counterdrill Symbol?
The symbol for a counterdrill is the same as a countersink (⌵) but there will be a depth
stated as well.
How Are Counterdrills Shown on Drawings?
Counterdrilled holes are shown on drawings as follows – the bottom section view
shows what the top dimension refers to.
A counterdrill can also be stated as C’DRILL or CDRILL on an engineering drawing.
Taper
What Is a Tapered Hole?
A tapered hole is one where the start diameter of the hole is a different to the end
diameter of the hole.
Below is a 3D model of a tapered hole next to the same hole cut in half:
What Is the Tapered Hole Symbol?
The taper symbol is:
How Are Tapered Holes Shown on Drawings?
Tapered holes can be shown in a number of different ways on engineering drawings.
An example of a drawing showing a tapered hole is below:
The taper in the above example is 1:5. The end diameter has been left on for reference
(in brackets).
To work out what the end diameter use the equation:
Tapered holes can also be shown without the taper symbol when dimensioning using
an angle is more important:
What Are Tapered Holes Used For?
Tapered holes have lots of different engineering applications.
A common example is using a tapered hole to secure cutting tools or other tool holders.
Screw Clearance
What Is a Screw Clearance Hole?
A screw clearance hole is exactly that.
It’s a simple hole that has a slightly bigger diameter than the screw thread so that the
screw can pass through.
What Is the Screw Clearance Symbol?
Screw clearance holes are shown as simple holes, and use the ‘Ø’ diameter symbol.
How Are Screw Clearance Holes Shown on Drawings?
Screw clearance holes are shown as simple holes:
What Size Screw Clearance Hole Should I Use?
You can use the metric guide for screw clearance holes or the imperial guide for screw
clearance holes.
What Are Screw Clearance Holes Used For?
Screw clearance holes are used for components that need the screw or bolt to go
through them.
An example of this is a bracket that needs to be attached to a block.
The bracket has screw clearance holes so that a bolt can pass through it.
The bolt is threaded into the block which has a tapped hole.
The compression force of tightening the bolt xes the bracket to the block.
Tapped Hole
What Is a Tapped Hole?
A tapped (or threaded) hole is a hole that has a thread.
What Is the Tapped Hole Symbol?
The symbol for a tapped hole depends on the standards used. For metric holes, the
diameter symbol is replaced with an ‘M’. For example a tapped hole for an M8 bolt
would be ‘M8’.
For different types of threads, for example a Uni ed National Fine (UNF) thread, the
numerical dimension is shown rst then the thread type “UNF”.
How Are Tapped Holes Shown on Drawings?
Tapped holes are shown on drawings as follows:
The “2.5” is the pitch of the thread, which is the distance in millimeters between each
thread.
For a UNF thread, a through 1½” 12 hole would look like this:
The ’12’ means that there are 12 threads per inch.
What Are Tapped Holes Used For?
Tapped holes are used to hold threaded components. Examples include screws, bolts
and threaded rods.
Enjoyed this post? Check out our types of welds post.
Conclusion
We hope you enjoyed our new types of holes guide.
Now we’d like to hear what you have to say:
Which type of hole did you learn today?
Or which type of hole do you use most often?
Let us know by leaving a comment below right now.
25 Comments



25 thoughts on “Types of Holes – The Complete Guide”
JOHN
22 NOVEMBER 2021 AT 10:25
Thanks for this info. Been a while.
Reply
THE ENGINEER
23 DECEMBER 2021 AT 18:25
Thanks John, glad you enjoyed it!
Reply
GAURAV PATEL
27 APRIL 2023 AT 09:27
Very useful article
❤❤.
Reply
VALERIY
4 DECEMBER 2021 AT 09:02
Very useful article!
Thanks
Reply
THE ENGINEER
23 DECEMBER 2021 AT 18:26
Thanks Valeriy!
Reply
NICK
20 DECEMBER 2021 AT 08:19
If I have a tapped hole and counter bore feature on the periphery of a round face,
would the tapped hole depth still start from the imaginary arc, or from the bottom
of the counter bore? I can’t nd any speci c drafting standard that shows this but
looking at the spot face example, it would seem that the tapped hole depth would
be understood to start from the circular face, and not the rst at face at the
bottom of the counter bore?
Reply
THE ENGINEER
23 DECEMBER 2021 AT 18:23
Hi Nick, great question.
Usually the smaller diameter (pilot) hole is the rst dimension given for a
counterbored hole, and this is the same for a hole with a spotface (i.e. the
M20 hole dimension comes before the 50 mm diameter spotface dimension
above).
A good way to imagine this is as if you are machining the tapped hole rst and
then the spotface (so the tapped hole starts at the imaginary arc in your
example).
To stop any potential ambiguity in the engineering drawing of your imaginary
arc example, a section view with individual dimensions for the depth could be
used instead.
Reply
LY
30 DECEMBER 2021 AT 01:29
Is it a through hole through which cables go?
Reply
THE ENGINEER
30 DECEMBER 2021 AT 09:08
It depends on if the cables go through the whole component or not. If using
electrical conduit then this pipe could be seen as a through hole for the cable.
If the cable does not go all the way through the component, such as the hole
for a hotend sensor in a 3D printer heater block, then this would be a blind
hole.
Reply
NAGMA
11 JANUARY 2022 AT 07:14
Thanks a lot for Detailed explain along with 3D
Reply
THE ENGINEER
11 JANUARY 2022 AT 19:47
You’re welcome Nagma, glad you enjoyed the 3D CAD models!
Reply
TUONG
15 MAY 2022 AT 13:55
what does C’Drill (Only K ) mean? please help.
Reply
THE ENGINEER'S BIBLE
8 JUNE 2022 AT 20:44
Hi Tuong, C’Drill is referencing a counterdrilled hole and this article has now
been updated to explain counterdrilled holes.
It’s hard to say what the ‘Only K’ is refering to without seeing the drawing.
Perhaps it’s just the one instance to be counterdrilled?
Reply
MELLO
7 JUNE 2022 AT 07:11
Hello po ,what other term for counterdrill holes?
Reply
THE ENGINEER'S BIBLE
8 JUNE 2022 AT 20:46
Hi Mello, another term for a counterdrill hole could be “C’Drill” or “CDRILL” on
an engineering drawing.
We have added another 3D model to explain counterdrilled holes in more
detail.
Reply
MOHAMED
7 AUGUST 2022 AT 15:17
Thanks you. very well explained.
Reply
PARITOSH
24 DECEMBER 2022 AT 12:50
What is meaning of H7, if wirte as
“dia 16 H7 thru”
Reply
THE ENGINEER'S BIBLE
4 JANUARY 2023 AT 19:52
Hi Paritosh!
“H7” is the tolerance of the diameter of the hole. If using an ISO limits and ts
table, this means that the nal measured diameter of the hole needs to be
between 16.018 mm and 16.000 mm.
Reply
TOKIW
4 FEBRUARY 2023 AT 23:24
Can someone explain the following?
Ø5.5±0.04 ↧ – A – (10.12)
As I understand, it means that the depth of the given hole is until datum A and than
the dimension in parenthesses provides the estimated value in mm? Am I correct?
Reply
CHRIS
26 APRIL 2023 AT 02:22
I’ve learned a lot thanks!
Reply
THE ENGINEER'S BIBLE
26 APRIL 2023 AT 13:21
That’s great to hear Chris
😊
Reply
RAJ
12 AUGUST 2023 AT 04:04
simple explanation with clear diagram.
Reply
VINCENT
14 AUGUST 2023 AT 06:49
wow this website helps me a lot at my school, thank you so much !!
Reply
FORTUNE
23 AUGUST 2023 AT 06:06
Love this,thanks
Reply
JIM WALTON
8 MARCH 2024 AT 14:50
Thanks
Reply
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