Counterborekit

In this drawing the hole callout shows the hole and the tapping. The tapped hole is made using the Metric Standard. This is shown by ‘M’ followed by the diameter, tolerance, depth symbol and depth in mm.

An interrupted hole is any hole that is interrupted by another feature. This can be another hole or any other part feature like an extrusion. Interrupted holes are cut using a drill or milling tool. All holes are coaxial and drilled in features in a single sequence. Where there is no material, the tool passes straight to the next feature.

Tapered hole has a diameter changes as the hole progresses. Tapered hole usually gets narrower down the depth of the hole

Counterborevs countersink

Threaded holes are identified on engineering drawings using the Metric Standard. Often shown by an M where a thread is present.

A hole in engineering is a circle cut out or an opening in an object. In engineering holes can be drilled, punched or made using a rotating part fed into a stationary cutting tool. It’s important to note here that hole features are completely dependent on the type and shape of the cutting tool.

Simple holes are commonly used for fastening. These holes are great for holding temporary plastic fasteners. In addition to this, they can also hold bolts and screws and act as assembly points.

Counterdrilled holes have the same callout symbol as a countersink hole or a counterbore. The difference is that there is a depth mentioned with counterdrilled holes.

A tapped hole only functions as a fastening component. Threads can hold screws and bolts and are often used to join two parts using a threaded fastener.

Counterboredrill

A through hole extends from one side of the object and passes through to the other side. A through hole is open on both ends.

I’ve been interpreting drawings and symbols easily with a small intuition that I’ll share with you, which will help you identify callout symbols of holes, their use and difference between them.

Any hole with a constant diameter attached to another hole with a larger diameter above it is called a counterbore hole. The purpose of the larger hole above is to hide the screw head.

Counterborehole

Threaded hole is a more generic term used for any hole with internal threads. Threads can be made using dies, taps and thread milling cycle.

Simple holes are also used in certain assemblies to provide a passage for air or fluid. They are also used to align multi-part assemblies.

The callout symbol is its diameter ‘Ø’ and a depth symbol. These symbols have the corresponding measurements specified in the callout.

On a technical drawing, countersink hole is read using the ‘⌵’ callout. 17.30 is the theoretical edge for an M8 countersunk hole. 90° is the angle between the two edges of the cone shaped hole.

Threaded hole as the name suggests is any hole with threads. Threaded hole and tapped hole are often used interchangeably. Threaded hole has screw threads cut into it using a threading tool called tap. Tapping is the process of threading blind holes and the threaded depth can vary from below the surface to through the material.

For this drawing both holes are flat holes meaning their ends are not tapered or showing a conical ending, which is more commonly seen on drawings. (Conical and flat holes will be discussed in blind holes)

Threaded holes are made for bolts and screw thread assemblies. There are many types of threaded fasteners that can hold threaded components by screwing into the threads tightly. Threaded holes are reusable and made for components that need to be disassembled at some point.

Counterboresymbol

Countersunk holes are used with countersunk bolts for a smooth and flat surface. Countersink hole making is a fairly tedious process and requires precision cnc milling machines. These holes are diverse and can be made in any material including fiberglass, wood and metal.

Holes mirror the diameter, depth and geometry of the tool. When a hole is drilled to a certain depth, which is less than the depth of the object, it’s called a blind hole and when the hole passes from both sides of the object, it’s called a through hole.

Before we delve into the common types of holes. I’ll start with a simple hole that will help you understand all the other holes and their callout symbols.

Counterboretool

Tapped holes have threads that run along the depth of the hole. These internal threads are cut inside the holes and the process that creates a tapped hole is called tapping. These threaded holes can be identified easily by spotting internal grooves.

Bore, Counterbore, Drilled holes and many other types of holes are used in engineering. If you’re confused by their symbols, can’t identify them in engineering drawings and are simply unaware of what are the different types of holes in engineering? then this guide is for you!

Counterboredrawing

Sometimes, threads in metric can be shown as M20 x 3. Here 3 is the pitch of the thread. Pitch is the distance between successive threads.

A screw clearance hole doesn’t allow the screw head to pass and only differs from a standard screw hole by a slightly larger diameter.

A tapped hole can have different callouts. Tapped holes are usually made according to standard bolts and screws available in the market. As such, tapped hole callouts follow a given standard. The most commonly used standard for a tapped hole is Metric. Here, the information for a tapped hole is represented slightly differently.

In this drawing a 20 mm diameter hole that passes through the object is represented by Ø 20.00 Through and another hole with 30.00 mm depth.

Screw clearance holes allow the bolt or screw to pass through with ease. Screw clearance holes or clearance holes have slightly bigger diameter than the screw shank. The bolt passes through without making contact with the material and is usually caught on the other end by a nut and tightened.

CounterboreBit

Simple holes that pass through both sides of the object are through holes whereas, holes that do not pass all the way are called blind holes.

The second line shows the counterbore hole with counterbore symbol ⌴ and counterbore diameter of 23.79 mm with a thickness or depth of 7.50 mm.

Counterdrilled hole provides seamless finish for bolts and fasteners. The can also allow space for a rubber seal between the fastner and object.

Spotface holes have a small counterbore hole on top of a drilled hole. This larger shallow hole is great for stress distribution and holding washers.

First blind hole has a curved ending, which is typical for dowel holes. Most machining methods to make holes often leave a curved or conical end. You’re more likely to see holes of the first type.

A blind hole is any cut out in a material that does not pass through the material. Blind holes are always drilled or milled to a certain depth inside the material. They are closed on one end and have an opening on the other end.

There’s no specific callout for interrupted holes and depending on the types of holes drilled, the standard callouts of other holes can be used.

Any hole with a constant diameter attached to another hole with a larger diameter above it is called a counterbore hole. The purpose of the larger hole above is to hide the screw head.