Countersinks – All About

What is a countersink?

A countersink is an angled taper applied to a hole that allows a fastener (usually a flat head screw or similar) to sit even with, or below the surface which has been countersunk. Occasionally, a countersink is used simply as a method of chamfering or deburring a hole.

Countersink symbol

Countersink Blueprint GD&T Symbol two lines pointing down

The GD&T callout for a countersink is shown below. Some older blueprints may use the notation CSK to identify a countersink dimension.

If you want to type the ⌵ symbol, hold the ALT key and press 9013. See this list for other common keyboard shortcuts for GD&T and blueprint symbols.

How to dimension a countersink

countersink blueprint example

A countersink is dimensioned by specifying the diameter of the countersink where it meets the surface and the included angle. In the above example, the part has a 0.5 thru hole and a countersink with a diameter of 0.7 and an included angle of 82°.

How to measure a countersink

Countersinks can be measured by many different gauges. The easiest tool to use, assuming the tolerances aren’t too tight, is a pocket comparator with a reticle. Optical comparators and CMMs are regularly used to measure countersinks with very tight tolerances.

What does a countersink look like?

countersink example on part

Countersink vs chamfer

A countersink and a chamfer are very similar. A countersink is basically no different than a chamfer on a hole.

The main difference is that a chamfer is normally thought of as being at 45 degrees (though the angle can vary). A countersink is usually one of many different standard angle sizes.

The most common countersink angles are 82°, 90° or 100°.

Note that in the case of the 90° countersink, this callout is the same as a 45° chamfer because the countersink angle takes both sides into account, so it is twice the chamfer angle.

Countersink vs counterbore

cutaway examples of countersink and counterbore

The difference between a countersink and a counterbore is that a countersink has an angled bottom and a counterbore has a flat bottom. Countersinks are often used to recess a flat head screw. Counterbores are used to recess bolts, washers and other fasteners.

Countersink vs spotface

spotface example on part
Spotface example

A spotface has a flat bottom like a counterbore while a countersink is angled. A spotface is used to create a flat area in a specific location to allow a fastener such as a screw or bolt to sit squarely.

Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And readers get an exclusive discount on training!

Counterbores – All About

What is a counterbore?

A counterbore is a circular hole with a flat bottom which coincides with another hole. The counterbored section allows a bolt head or other fastener to be recessed.

What does a counterbore look like?

counterbore on metal part
An example of a counterbore in a piece of metal

Counterbore symbol

The GD&T callout for a counterbore is shown below. The counterbore symbol will often be used together with the diameter symbol and the depth symbol. Older blueprints may specify a counterbore with the notation CBORE instead of the counterbore symbol.

Counterbore Blueprint GD&T Symbol u shape
Counterbore symbol

If you want to type the ⌴ symbol, hold the ALT key and press 9012. See this list for other common keyboard shortcuts for GD&T and blueprint symbols.

How to dimension a counterbore

Diameter Blueprint GD&T Symbol o with line through it
Diameter symbol
Depth Blueprint GD&T Symbol line with arrow pointing down
Depth of symbol

A counterbore is dimensioned by including the diameter of the counterbore along with specifying the depth. The two ways to specify the depth are to specify how deep the counterbore is or the thickness of the remaining material. Both methods are acceptable and commonly seen.

In the example below, the part has a .250 hole and a .500 diameter counterbore to a depth of .100.

counterbore blueprint example

How to measure a counterbore

Counterbores can be measured with many different types of gauges. The simplest inspection tool to use, assuming the tolerances aren’t too tight, would be a caliper.

Pocket comparators, gage pins, and depth micrometers are other types of measuring equipment that are frequently used to measure counterbores.

Counterbore vs countersink

cutaway examples of countersink and counterbore

The difference between a countersink and a counterbore is that a countersink has an angled bottom and a counterbore has a flat bottom. The angle of the countersink can vary with many different angles used such as 82°, 90° and 100°.

Counterbore vs spotface

spotface example on part

A counterbore and a spotface are very similar. A counterbore is used to recess a fastener while a spotface is used to create a flat surface located allow a fastener to be used. A spotface is used to let a fastener sit flat and in a specific location. A spotface is basically a shallow counterbore.

Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And readers get an exclusive discount on training!

Tolerance Blocks – All About

What is a tolerance block?

The definition of a tolerance block is a section on an engineering drawing or blueprint that identifies tolerances for a dimension that aren’t specifically called out on the print. Notice how the 17.5 dimension below has a tolerance directly associated with it.

Now look at the 12.5 dimension and notice that no tolerance is specified. Because there is no tolerance called out, the tolerance in a tolerance block (general tolerances) would be applied to this specific dimension.

Note: The contents of the tolerance block are often referred to as the general tolerances. Depending on the units used on the blueprint, the tolerance block can be specified in metric or imperial (inch) units.

Tolerance block examples

tolerance block example

How to read a tolerance block

Most tolerance blocks are identified based on the number of decimal places of the feature on the blueprint. 

Using our previous examples again, notice that the 12.5 dimension has one number after the decimal place. Based on the tolerance block, this would assign the +/- 1 mm tolerance to the dimension. 

If the dimension was instead 12.54 then the tolerance assigned would be +/- .5mm. Angular dimensions often are specified in the same way. In our example, all unspecified angular tolerances would be assigned the =/- .5° tolerance.

tolerance block example

Other names for a tolerance block

  • Default tolerances
  • General tolerances
  • Standard tolerances
  • Title block tolerances

Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And readers get an exclusive discount on training!

Related articles

EAGems 0-6″ Digital Caliper Review

EAGems Caliper with case
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IP54 protection rating
Two year warranty extended to three if registered
Responsive customer service

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Stainless steel jaws


The EAGems 0-6” digital caliper is a good value for the price. Made of stainless steel, it takes measurements in inch, metric and fractional units. The fractional unit mode is especially useful for those looking to use this caliper for woodworking inspection. Boasting an accuracy of +/- .0005”, .01mm or 1/64th of an inch, the EAGems caliper is in line with most other tools in the price range and even some that are more expensive. The included thumb roller on the tool makes it easier to take measurements. Often calipers in a cheaper price range such as this one will lack this feature. Combined with the measurement lock feature, this competes with much more expensive digital calipers such as the Mitutoyo 500-196-30 0-6” Digital Caliper. The EAGems (which is short for Edward Allen Gems) caliper is capable of taking inside, outside, depth and step measurements to the noted accuracy.

EAGems caliper display

The large, easy to read display takes a little getting used to because the fractional display makes the last two digits smaller. The display has an automatic on/off feature which is designed to save battery life. Depending on the level of use, the typical battery will last about a year. Speaking of batteries, the caliper comes with an extra battery to give the user approximately 2 years of battery life out of the box.

EAGems caliper features

Battery replacement for the caliper is a simple task. To replace the battery of the caliper, use the included screwdriver to remove the screw from the back of the tool and swap out with the included extra battery or another purchased battery.

ingress protection (IP) ratings solids description
ingress protection (IP) ratings liquid protection

One of the best features of the EAGems caliper is the IP54 rating. Uncommon for a tool at this price point, the IP54 rating means that the caliper is protected against dust but not completely dust tight and protected against splashing water. Practically, this means the tool is resistant to most forms of normal contamination such as a coolant splash.


For the price, the EAGems 0-6” digital caliper is a great tool. If you are looking for a quality measuring tool that won’t break the bank, keep this one in mind. While a caliper made by brands such as Mitutoyo might have a more proven level of reliability, this caliper is almost as good for about a third of the price. Don’t overlook the importance of the IP54 protection rating if you are going to be working in a very dusty environment or around splashing coolant. This is a valuable feature not included on many calipers that cost much more.

Full Radius – All About

What is a full radius?

A full radius is a radius that smoothly blends into another surface. Full radius is most often specified in a rounded slot feature or a feature that mimics a rounded slot.

A full radius sometimes noted as a true radius or full R is outdated language and not part of the current revision of the drawing standard ASME Y14.5. The full radius callout is referencing a smooth transition from the radius to an adjacent surface.

full radius blueprint example

How to measure a full radius

Because no reference standard documents the requirements of a full radius, there are no specific requirements for the callout.

When a full radius, true radius or full R is called out on the drawing, the blueprint drafter is attempting to control the blend into and out of the specified radius.

Full radius vs radius

There is no difference between the drawing callouts of full radius, true radius and radius. Because there are no specific requirements for a full radius referenced by any drawing or GD&T standards, there is no difference in the requirements of a full radius or full R vs a radius or R. A full radius does not have a tolerance. A radius if drawn correctly will have some form of a +/- tolerance or be controlled through a GD&T requirement such as profile or cylindricity.

There is no difference between the requirements of the example below or the previous one.

full radius blueprint example

Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And readers get an exclusive discount on training!

Related Articles

TYP & Typical on Blueprints [What They Mean & How to Inspect Them]

What does typical mean on a blueprint?

Typical on an engineering drawing identifies a repeated feature. This is identical to a feature which is identified as 2x or 5x. 

A typical dimension callout will occasionally be followed by a 2x, 5x or similar, to specify the quantity of features which are tolerance the same. 

The typical callout will most often be used as part of a repeating pattern such as a bolt hole circle, to identify the hole sizes or angle between the holes. 

Another common application is to identify a common chamfer size on a component. It should be noted that the notation of “typical” is not a part of the current revision of the ASME Y14.5 standard and therefore not a recommended notation for use on an engineering drawing. There are however countless blueprints in the wild which may already use this language.

What is the symbol for a typical dimension?

There is no GD&T symbol for a typical dimension. A typical dimension callout is identified with either TYP. or TYPICAL. In the example below, the typical notation is used to reference that the slot on both sides of the part is to be machined to the same depth.

typical callout blueprint example

A better way to identify the same dimension would be as shown below. It is best to not leave anything to the imagination of the person interpreting the blueprint.

slot depth blueprint example

Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And readers get an exclusive discount on training!

Rexbeti 0-1″ Digital Micrometer Review

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Cheap price

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Few extra features


Rexbeti isn’t exactly a household name when it comes to inspection tools such as this 0-1” digital micrometer. What it lacks in name recognition, it makes up for in price but the question is can the quality keep up?
The Rexbeti 0-1” digital micrometer has a .00005” or .001mm resolution which is standard for most digital micrometers. It has an accuracy of +/- .0001” which is only slightly worse than some of the best digital mics such as this one from Mitutoyo but better than most budget options. Prices fluctuate some but the Rexbeti sacrifices very little in accuracy while cutting the cost dramatically.
The digital readout on this set of micrometers is large and easy to read. The display has a simple button layout with only 3 buttons on the face. These primary buttons are on/off, one for switching units between inches and millimeters, and one for zeroing the tool.

The Rexbeti 0-1” digital micrometer features a ratchet stop for taking consistent measurements. The ratchet stop when used correctly allows the user to exert a controlled amount of force when taking readings. This results in more accurate and consistent measurements. Additionally, when not in use this digital mic has an auto shut off feature to save battery life. The tool also comes with an extra battery and a protective case for storage.


Beyond these simple features this Rexbeti micrometer doesn’t have anything too fancy going on. What it lacks in extras though, it makes up for in accuracy. When compared to many other budget digital micrometers, its accuracy stands out for the price. These Rexbeti 0-1” digital micrometers are a great buy at the price and capable of measuring up to all but the most precise digital micrometers.

iGaging 0-1″ Digital Micrometer Review

igaging digital micrometer
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Extra features

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Battery life


iGaging is a popular brand for budget friendly inspection tools. This set of digital micrometers is no different. They have a measuring resolution of .00005” or .001mm and an accuracy of +/- .00015” which equates to +/- .003mm. While not as good as some digital micrometers which cost 2-3 times as much, the iGaging digital mics come close at a fraction of the price.
ball attachment for igaging digital micrometer
These iGaging digital micrometers have a very impressive feature set. Some of the extras that aren’t normally seen in its price range are a SPC output and a ball attachment for the anvil. The SPC output allows you to record measurements directly to your computer while the ball attachment allows you to measure round surfaces such as the wall thickness of tubing. Some of the more standard type features include an extra battery and a protective case to keep your tool safe. Carbide tips are a nice bonus that isn’t always seen on budget level digital micrometers. They provide superior wear resistance when compared to normal hardened steel.
A decent size display and simple button layout adorn the face of the tool. With the press of a button the micrometer switches units from inches to millimeters. The ability to switch between absolute and incremental measuring modes is available too. Nothing too out of the ordinary present in the normal use of the mic.
Like most other digital micrometers, this one from iGaging has a little more weight to it than a standard micrometer. Some don’t like the added weight because they feel it makes it harder to maneuver around their workpiece. With a little time and use, I don’t believe the weight will bother anyone.
Now onto some of the negatives. The biggest problem is that some buyers report instances of the display flickering. All of the budget digital micrometers have quality issues such as this one, the bigger problem is that the manufacturer isn’t the most responsive to problems. Another common issue for lower priced tools is limited battery life. For most this shouldn’t be too much of a bother but it’s best to keep an extra battery or two on hand. Lastly, the thimble feels cheap because of the plastic material used.
igaging digital micrometer in case


The simplicity of the display and button layout are a nice touch and will be appreciated by those not as familiar with digital micrometers. The addition of the SPC output and ball attachment put these mics a step above most other entry level digital micrometers. To get a better micrometer you will need to pay 3 times the cost of these mics or more. The iGaging 0-1” digital micrometer is a solid budget priced inspection tool.

Engineering, Manufacturing and Quality Abbreviations and Acronyms

abbreviations and acronyms word bubble

OMG why are there so many acronyms and abbreviations? FYI here is a huge list of common meanings. Hopefully it helps decipher some of the jargon and gibberish. 

8D – method of problem solving commonly used in the automotive industry.

AQL – acceptance quality limit, previously acceptable quality limit

APQP – advanced quality product planning

AS9100 – aerospace quality standard

ATP – acceptance test procedure

BOM – bill of materials

CAD – computer aided design

CAGE – Commercial and Government Entity code

CAM – computer aided manufacturing

CAPA – corrective and preventive action

CAR – corrective action report

CFE – customer furnished equipment

CFM – customer furnished material

CNC – computer numerical control

COA/C of A – certificate of analysis

COC/C of C – certificate of conformance or certificate of compliance

COTS – commercial off the shelf

CSM – customer supplied material

CT – center thickness

DFARS – Defense Federal Acquisition Regulation Supplement

DFMEA – design failure mode effects analysis

DPA – destructive physical analysis

DPAS – Defense Property Accountability System

DPPM – defective parts per million

DSS – data summary sheet

ECN – engineering change notice

EIDP – end item data package

ERP – enterprise resource planning

ESD – electrostatic discharge

ETV – edge thickness variation

FAI – first article inspection

FAIR – first article inspection report

FMEA – failure mode and effects analysis

FOB – free on board

FOD – foreign object damage

FW – face width

GFE – government furnished equipment

GFM – government furnished material

GFP – government furnished property

GIDEP – government industry data exchange program

GMIP – government mandatory inspection points

GSI – government source inspection

GSS – government source surveillance

HIC – humidity indicator card

IAQG – International Aerospace Quality Group

IAW – in accordance with

IOT – internet of things

ISO – International Organization for Standardization

ITAR – International Traffic in Arms Regulation

JIT – just in time

KPI – key performance indicator

MBB – moisture barrier bag

MRB – material review board

MSDS – material safety data sheet

NADCAP – National Aerospace and Defense Contractors Accreditation Program

NC – non conformance

NCM – non conforming material

NDT – non destructive testing

NIST – National Institute of Standards and Technology

OCM – original component manufacturer

OD – outside diameter

ODM – original design manufacturer

OEM – original equipment manufacturer

OTD – on-time delivery

PCB – printed circuit board

PDCA – plan, do, check, act

PEM – plastic encapsulated microcircuits

PFMEA – process failure mode and effects analysis

PID – product identification document

PL – parts list

PM – preventative maintenance

PPAP – Production Part Approval Process

PO – purchase order

QA – quality assurance

QAPP – quality assurance program plan

QC – quality control

QML – qualified manufacturers list

QPL – qualified product list

QTP – qualification test plan

QTR – qualification test report

RCA – root cause analysis

REACH – registration, evaluation, authorization and restriction of chemicals

RFI – request for information

RFQ – request for quote

RMA – return material authorization

RoHS – Restriction of Hazardous Substances

SCAR – supplier corrective action request

SDS – safety data sheets

SMP – supplier management process

SOP – standard operating procedure

SOW – scope of work

SPC – statistical process control

TDP – technical data package

TIR – total indicator runout

WI – work instruction

WIP – work in progress

XRF – x-ray fluorescence

Ballooning/Numbering A Blueprint

What is a ballooned or numbered blueprint?

ballooned drawing example

Commonly referred to by many different names including ballooned drawing, bubble drawing, numbered print, etc. A numbered drawing or blueprint is a way to identify individual attributes of a part or assembly as depicted in an engineering drawing. The numbers and balloons or bubbles are ordinarily done in red ink or a red font as seen above.

What are ballooned drawings used for?

Numbered drawings are a common component in the inspection process. They can be a part of your in house inspection procedure or a requirement which you provide to your customers. Ballooned drawings are also frequently used as part of a first article inspection report package. They allow the reader to connect an individual measurement to its location on the blueprint. This is especially handy when multiple attributes with the same nominal values are present.

How to number a drawing

Numbering or ballooning a blueprint is a process that has some flexibility to the order in which attributes are labeled. The most important aspect is that all attributes are assigned a number including all notes and general tolerances as needed. When in doubt, number it. Where to start is a matter of preference but make sure that your numbering sequence is easy to follow. Generally the person numbering the drawing will start in the top left view and work their way clockwise assigning numbers to attributes in that particular view. This process is repeated for all views present on the drawing in a top to bottom, left to right manner similar to the way you read a book. Some users will list attributes in the notes first such as material, but this is simply a matter of preference. Just make sure to number all the relevant attributes in the notes. If you work in a logical manner, it will be much easier for the customer or reader to follow along.

Example of a fully numbered drawing

What to include in a numbered drawing

Assign a number to every attribute on the print including all notes and applicable general tolerances. Some notes may include more than one attribute in a single note which requires a numbered attribute.

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