Nuts and Bolts 

Units of Measure


•   United states customary (USC)


–   Linear examples: inch, foot, yard, mile

–  Weight examples: ounce, pound, ton

–  Temperature example: Fahrenheit

–  Pressure examples: pounds per square inch

–  Torque example: foot pounds


• Metric


–  Linear examples: meter, centimeter, kilometer

–  Weight examples: grams, kilograms

–  Temperature example: Celsius

–  Pressure examples: kilogram per square centimeter, bar

–  Torque example: Newton meters








•  Fasteners are those things used to secure or hold parts of something together.

–   One type of fastener most commonly used is the threaded fastener.








Bolt Identification

Bolt Identification


•   Bolt head

–  Used to loosen and tighten the bolt.


•   Diameter

–  Measured across the threaded area


•  Thread pitch (English system)

–The number of threads per inch


•  Thread pitch (Metric system)

–The distance in millimeters between two adjacent threads



Imperial Size Bolt Identification Example


•  An Imperial size bolt that is identified as 3/8" x 2" x 24:

–  Has a shank diameter of 3/8 inch.

Bolt size


–  Is 2 inches long from the bottom of the head to the end of the shank.

–  Has 24 threads per inch.








Metric Size Bolt Identification Example

  • A metric size bolt that is identified as:  

              -   6mm x 30mm x 1.25mm:

–  Has a shank diameter of 6 millimeters.

–  Is 30 millimeters long from the bottom of the head to the end of the shank.

–  Has a distance of 1.25 millimeters between its threads.




Bolt Grade Markings

Bolt Grade Markings


•   Customary (inch) bolts

–  Identification marks correspond to bolt strength.

–  Increasing numbers represent increasing strength.


•   Metric bolts

–  Identification class numbers  correspond to bolt strength.

–  Increasing numbers represent increasing strength.



Tightening Bolts


•  Any fastener is near worthless if it is not as tight as it should be.


•  When a bolt is properly tightened, it will be “spring loaded” against the part it is holding.


•  This spring effect is caused by the stretch of the bolt when it is tightened.


•  Normally a properly tightened bolt is stretched to 70% of its elastic limit.


–  The elastic limit of a bolt is that point of stretch from which the bolt will not return to its original shape when it is loosened.

–  Not only will an over tightened or stretched bolt not have sufficient clamping force, it will also have distorted threads.

–  The stretched threads will make it more difficult to screw and unscrew the bolt or a nut on the bolt.





•  Many different types of washers are used with fasteners.



•  The type of washer defines the purpose of the washer.

–Flat washer  


•  used to spread out the load of tightening a nut or bolt.

•  This also stops the bolt head or nut from digging into the surface as it is tightened.

Lock washers 


•  Used to lock the head of a bolt or nut to the work piece to keep it from coming loose.


Thread Lubricants and Sealants


Thread Sealant

•  Thread Sealant:


–  Used on bolts that are tightened into an oil or coolant passage.

–  The sealant prevents the liquid from seeping past the threads.







•  Thread Lockers:


Thread Locker


–  Prevent a bolt from working loose as the engine or other part vibrates.