Fastners And Threads Flashcards
What is a fasteners?
A device used to fasten or connect two pieces of material to form one simple unit.
What are the (6) purposes of threads
- Transmit power
- Control movement
- Convey material
- Hold parts together
- Form a pressure tight joint
- For measuring
Threads on the outside of a fastener or part are called ____________
External threads
Threads on the inside of a cylinder are _____________
Internal threads
The distance between two screw threads measured parallel to the axis is called ____________
Pitch
The largest diameter of a screw thread (both internal and external) is called _________________
Major diameter
The smallest diameter of a screw thread (both internal and external) is called _____________
Minor diameter
Diameter by which the fastener is named; not it’s exact measurement is called _____________
Nominal diameter
The diameter of the surface of an imaginary coaxial cylinder that passes through the thread profile at such points as to make the width of the thread equal to the width of the groove is called the ___________
Pitch diameter (effective diameter)
The distance a screw thread advances axially in one turn is called the __________
Lead
On a _________ start screw thread the lead is the same as the pitch
Single start
On a ________ start screw thread the lead is twice the pitch
Two start
The top surface joining adjacent sides or flanks of the thread; this may be flat, rounded, or sharp is called the ________
Crest
The bottom surface joint adjacent sides or flanks of the thread; this may be flat, rounded, or sharp is called the _________
Root
The surface of thread connecting the crest to the root is called the _________
Side or flank
The distance from the crest to the root, measured perpendicular to the axis is called the ____________
Single depth of thread
The distance between the adjacent sides of the thread, measured along the pitch line is called the ___________
Thickness of thread
The relationship between two mating parts with respect to the amount of clearance when they are assembled, or with respect to the amount of interference preventing assembly is called ____________
The fit
The total permissible castigation, represented by the given maximum and minimum sizes of the parts is called the ____________
Tolerance
An internationally agreed difference in the dimensions of mating parts is called ____________
Allowance
The angle that is formed by the sides or flanks of a screw thread. Is called the ____________
Thread angle
Most fasteners have a ______ thread angle
60 degree
The angle formed by the helix of slope of the thread realities to the thread axis is called the ______________
Helix angle
A screw thread is considered to be right hand if when viewed from either end the screw threads winds in a ___________ direction
Clockwise
If a screw thread can be viewed from either end winds counter clock wise the thread is __________
Left hand
LH refers to
Left hand
For applications involving a counterclockwise rotation a ___________ is needed to get a secure lock
Left hand thread (LH)
A single start screw consists of __________ and groove
A single ridge and groove
A double start thread has ___________ and grooves
Two ridges and grooves
A triple thread has ___________ starting at equally spaced points around the circumference
Three grooves
Why would an object would require multiple threads?
To increase lead without weakening the shaft by an increase of pitch depth
Nominal size of a fastener is normally referring to the _______________ and the ___________ measurements on a fastener
Major diameter and the length
The length of a fastener is taken from?
The length of the shank, threaded section and chamfer
T or F
All threads in an assembly take equal amounts of load
False
The first full thread to the flat washer takes 50% the next thread takes 25% and the remaining 25% is shared across the remaining threads
The first full thread to the flat washer takes ____ % the next thread takes ___% and the remaining ____% is shared across the remaining threads
50%
25%
25%
3/4” - 10 unc- 2A x 1 1/2”
What is the number of threads?
10 threads per inch (tpi)
3/4” - 10 unc- 2A x 1 1/2”
What refers to external or internal threads?
A - external (B = internal)
3/4” - 10 unc- 2A x 1 1/2”
What value refers to the nominal diameter?
3/4”
3/4” - 10 unc- 2A x 1 1/2”
Which value gives the length?
1 1/2” dp (depth of full threads in hole)
3/4” - 10 unc- 2A x 1 1/2”
What refers to the class of fit?
2 = class of fit (1-6)
2A and 2B in thread designation are sometimes not in the name for what reason?
Considered standard
What are the classes of Fit?
1-6 with 1 = max looseness and 6= max tightness
Where would a class 5 or 6 thread be used?
For extremely precise tools and high vibration conditions
What are the 4 designations for American national thread?
- National coarse (NC)
- National fine (NF)
- National extra fine (NEF)
- National Special (NS)
What are the 2 most used national threads?
NC (national coarse) and NF (national fine)
What are the 4 unified screw threads?
- Unified National Coarse (UNC)
- Unified National Fine (UFC)
- Unified national extra fine (UNEF)
- Unified National Special (UNS)
What is the difference in pitch between NF (national fine) and UNF (united National Fine) 1 inch
They have a different pitch on the 1 inch diameter.
UNF - 12 tpi
NF - 14 tpi
What is the difference between an American national thread bolt and a unified?
American national thread has flats on the crest and root
Unified thread has a rounded root and sometimes a rounded crest
Where is acme thread used?
Used for adjusting and positioning screws on a machine it is NOT for fastening.
What are the characteristics of a acme thread?
Flat crest and roots
29 degree included angle
Crest and root have slightly different widths
What is the reason for national pipe taper (NPT) thread?
To seal joints and prevent leakage.
What is the taper on pipe thread?
3/4” taper per foot
What does ISO stand for ?
International Organization for standardization (ISO)
Threaded fasteners are categorized in what 3 categories?
- Studs
- Screws
- Bolts
What is the difference between a screw and bolt load?
Screw is loaded by a head and a bolt is loaded or tightened by a nut. Although some can be used either way
Bolts, nuts, and cap screws are classified in what 3 ways?
- Tensile strength
- Design (shape)
- Size and thread pitch
What is the most common material a threaded fastener is made from?
Steel
What is tensile strength?
The ability of a material to resist forces that tend to pull it apart.
How do you identify the tensile strength of a fastener?
Grade markings are stamped on their heads during manufacturing.
In the metric system how can you tell what fasteners have a better tensile strength through their markings?
The lower number = lower strength
How do imperial fasteners distinguish their tensile strength?
Through slashes on the head
What are the 3 main bolt designs?
- Carriage
- hex headed
- square headed
Where are carriage bolts typically used?
Where smooth and round head is desired which adds additional security
What is the most common bolt design used?
Hex headed bolts
What are the benefits of hex headed bolts?
New surface area every 60 degrees
Can be more easily tightened in tight quarters
What are the 8 most common nut designs?
- Hex nut
- Square nut
- Slotted hex nut
- Castellated nut
- Stover nut
- Nylon lock nut
- Jam nut
- Palnut
_____________ nuts is the most general purpose nut used in almost any location where a strong nut is required and there is limited access
Hexagonal nut (hex nut)
____________ nuts are most often used in locations where access is unrestricted. They offer a larger flat surface for wrench jaws, and able to withstand greater torque.
Square nuts
__________ nuts are similar to hexagon except they are made to receive a cotter pin.
Slotted hex nuts
_________ are locking nuts that also use a cotter pin to prevent turning
Castellated nuts
___________ are self locking nuts that have their top inner surfaces bent inward. When the top part of the nut is tightened onto a bolt this oval part is forced back around causing resistance to turning.
Stover nut
___________ nuts are another type of self locking but. When the nut is tightened the nylon is forced to stretch causing resistance
Nylon lock but
__________ but are thinner than regular hex nuts and are used as a locking device. The nut should be between the hex nut and the surface so the hex nut takes the full bolt load
Jam nut
__________ are an even thinner version of the jam nut
Palnuts
The size of a nut or of any internal thread is identified what characteristics?
Major thread diameter and thread pitch of the bolt that would fit the nut.
What tool do you use to find a thread pitch?
Thread pitch gauge
What is the maximum diameter of a machine screw?
3/8
How do you find the diameter of a machine screw?
Multiply the screw number by 0.0013 and add 0.060
What are dowel pins primary purpose?
Aid in aligning two machinery parts
What is the primary purpose of shear pins?
To connect a gear or other part to a shaft they shear under too much pressure to prevent further damage.
How do shear pins break off?
They are either made of a softer metal or have grooves where they are designed to break
__________ is a hallow cylinder made of spring steel with a split lengthwise and beveled at each end. These are made slightly oversize to be compressed when driven into place.
Spring pin / rolled (coiled) pins
__________ solid pins with a slot along their length. On some pins the slot or groove runs the full length but only partly through the pin. They have tremendous holding pressure as they expand when driven into place
Grooved pin
How are grooved pins designated?
By type, nominal diameter, length, and material
What are the types of groove pins (names) ?
A-F
What are the two common types of convenience pins?
Spring locking pins
Quick lock pins
____________ used to hold other pins when they must be removed frequently
Spring locking pins (hairpin cotters)
_________ pin is used to secure removable attachments to a machine. Have a split steel ring mounted to one end.
Quick lock
What are the 3 types of taps?
Taper
Plug
Bottoming
How do you find the drill size for a M10 x 1.5 tap?
TDS = nominal diameter - pitch
=10-1.5
=8.5
What are the common methods for repairing badly damaged internal threads?
- Drill and tap the hole bigger
- Plug weld and re drill
- Thread restoring insert (helicoils)
What is preload in fasteners?
Tightening a nut and bolt assembly to a predetermined torque value to prepare it for an opposing load.
How are right hand and left hand threads identified?
Direction of threads.
LH = counter clockwise
RH = clockwise
What is the purpose of using multiple threads?
Spread up lead without weakening
