Fasteners and Threads Flashcards
Most fasteners have a thread angle of what?
60 degrees
The distance from point to point on a screw to a corresponding point on the next thread, measured parallel to the axis is called what?
The pitch
The distance a screw thread advances axially in one turn is called what?
The lead
The surface of a thread connecting the crest to the root is called what?
Flank or side
For counterclockwise rotation what kind of thread is used?
Left-hand thread
In threaded fasteners the first full thread of the nut next to the flat washer takes how much of the load?
50 percent, the next thread 25 percent, the remaining share the rest
What does 3/4” - 10 UNC - 2A x 1-1/2” lg mean?
3/4" nominal diameter 10 tpi Unified National Coarse thread style Class fit 2 A = external thread 1-1/2" length
Maximum looseness in the mating threads is what class?
Class 1
Average fit with little play in threads for everyday shop bolts are what class?
Class 2
No looseness in mating threads are which class?
Class 3
Precision threads in a micrometer is which class?
Class 4
Extremely precise threads are which class?
Class 5&6
60 degree thread angle with flats on the crest and root are which type of threads?
American National Threads - National Coarse and National Fine most common
60 degree thread angle with a rounded root are which type of thread?
Unified Screw Thread
The threads in this series have the same pitch for all diameters
Constant pitch series
This thread is not for a fastener, has flat crest and roots, and a 29 degree angle. Used on a lathe
Acme Thread
This tapered thread seals a joint, preventing leakage
National Pipe Taper (NPT)
M8 x 1.25 x 50 mm means?
Metric
8 - Nominal diameter
1.25 the pitch in mm
50mm - length
What the difference between a bolt and screw?
The screw is loaded by the head, and a bolt is loaded or tightened by a nut
A rod that is threaded on both ends is called what?
A stud
The head markings on a bolt head indicate what?
Tensile strength
What type of bolts are used when a smooth round head is required?
Carriage bolts
The most common bolt head is
Hexagon head bolts
These bolt heads must be turned 90 degrees before the wrench can be relocated on the head
Square headed bolts
Cap screws start at what size?
1/4”
This type of nut are locking nuts that also use a cotter pin
Castellated nut
These nuts withstand greater torque and a larger flat surface than a Hex nut
Square nut
When used to lock a regular nut the jam nut should be between the hex nut and joint surface because?
The hex nut takes the full bolt load
A thinner version of a jam nut is called?
Palnuts
The size of any internal thread is identified by what?
The major thread diameter and thread pitch of the bolt that would fit the nut
Machine screws come in sizes as big as
3/8”
How do you find that diameter of a machine screw?
Start as 0.060 and add 0.013 for every screw number increase
These are used under bolt heads to increase the bearing surface of the fastener and protect from damage
Flat plain washer
These washers are used to keep nuts and bolts from becoming loose from vibration
Split-ring lock washers
These are thicker and stronger than than Split washers
Hi-collar lock washers
These washers use teeth and are used when extra holding power is required
Tooth-lock washers
What is the ratio of a taper pin?
1/4” per foot (1:48)
What are used to align two machinery parts?
Dowel pins
These pins are designed to break under greater than normal loads
Shear pins
These pins are hollow, oversize and compress when driven into place to hold the parts in place
Spring pins and roll (coiled) pins
These pins expand when driven into place and have tremendous holding power
Grooved pins
These are used instead of cotter pins when they must be removed frequently
Spring-locking pins (hairpin cotters)
The three taps used for different stages of a cut
Taper, Plug, Bottoming
This is used to hold the tap securely and that even forces are applied
Tap wrenches
How do you determine the tap size of a hole?
Tap drill size = nominal diameter - pitch
Reminder, pitch =1/pitch
What are used to cut external threads?
A die
What is the proper process for using a tap?
Back a quarter turn, forward half a turn
What tool is used to hold a die?
Die stock
Elongation of the bolt is called
Tension
The tendency of the wedge shape of the thread to enlarge the diameter of the nut is called
Dilation
The amount a fastener can be stretched and still return to its original length is called
Elastic limit
Where the fastener begins to take a permanent set
Yield point
The failure or breaking point of a bolt
Ultimate tensile strength
Tensile forces are measured in
per square inch (psi)
Tightening a nut and bolt assembly to a predetermined torque value is known as
Preloading
These bolts provide visual evidence that the desired preload value has been reached
Preload indicating bolts
What are the types of torque wrenches?
Torque-limiting, dial indicating, deflecting beam
This toque wrench is used where high torque is required to tighten fasteners
Hydraulic torque wrench
