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Nuts and Bolts
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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 |
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Fasteners
• Fasteners are those things used to secure or hold parts of something together.
– One type of fastener most commonly used is the threaded fastener.
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Nuts
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Nuts are used with other threaded fasteners when the fastener is not threaded into a piece of work.
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The most common is the hex nut which is used with stud and bolts and is tightened with a wrench.
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Bolt Identification
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• 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.
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– 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
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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
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• 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 looseded.
- 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.
Washers
• Many different types of washers are used with fasteners.
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• The type of washer defines the purpose of the washer.
- Flat washer
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- 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
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- Used to lock the head of a bolt or nut to the work piece to keep it from coming loose.
Thread Lubricants and Sealants
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• 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:
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– Prevent a bolt from working loose as the engine or other part vibrate.
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