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Questions and Answers
What is the primary risk of using the wrong type of screwdriver or bit?
What is the primary risk of using the wrong type of screwdriver or bit?
What does the term 'AF' refer to in the context of fastening tools?
What does the term 'AF' refer to in the context of fastening tools?
Which type of fastener requires careful identification to avoid damage?
Which type of fastener requires careful identification to avoid damage?
What does a ¼ BSF spanner fit?
What does a ¼ BSF spanner fit?
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Which screwdriver bit should NOT be used on a Hi-Torque screw head?
Which screwdriver bit should NOT be used on a Hi-Torque screw head?
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What is one primary use of a cap nut?
What is one primary use of a cap nut?
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What happens to the shape of the Nyloc cap nut when it is screwed onto a bolt?
What happens to the shape of the Nyloc cap nut when it is screwed onto a bolt?
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Which feature of the lightweight stiffnut is critical to its design?
Which feature of the lightweight stiffnut is critical to its design?
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Which type of nut is used to avoid snagging passenger clothing?
Which type of nut is used to avoid snagging passenger clothing?
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What characteristic does the lightweight stiffnut have compared to larger nuts?
What characteristic does the lightweight stiffnut have compared to larger nuts?
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What is the primary material used for manufacturing split pins?
What is the primary material used for manufacturing split pins?
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What should be checked before fitting the nut on a drilled bolt?
What should be checked before fitting the nut on a drilled bolt?
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Which of the following is NOT a recommended practice for using split pins?
Which of the following is NOT a recommended practice for using split pins?
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What is the term used for split pins in the USA?
What is the term used for split pins in the USA?
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What is the purpose of turning the legs of the split pins?
What is the purpose of turning the legs of the split pins?
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When is it necessary to cut split pins to a suitable length?
When is it necessary to cut split pins to a suitable length?
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Which of the following practices is recommended after closing the legs of a split pin?
Which of the following practices is recommended after closing the legs of a split pin?
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What distinguishes method (C) of split pinning from methods (A) and (B)?
What distinguishes method (C) of split pinning from methods (A) and (B)?
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What type of threads is considered the norm for screws and bolts?
What type of threads is considered the norm for screws and bolts?
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What is the major diameter of a thread measured from?
What is the major diameter of a thread measured from?
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Which threads are commonly used to secure rotating parts?
Which threads are commonly used to secure rotating parts?
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What does the lead or thread pitch indicate?
What does the lead or thread pitch indicate?
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What commonly characterizes the root and crest form of threads?
What commonly characterizes the root and crest form of threads?
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What happens when the underside of the screw/bolt head bottoms against the mating surface?
What happens when the underside of the screw/bolt head bottoms against the mating surface?
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Which of the following describes left-handed threads?
Which of the following describes left-handed threads?
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Why is the production of correct radii in thread forming difficult?
Why is the production of correct radii in thread forming difficult?
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What is the purpose of a GO / NO GO plug gauge in thread gauging?
What is the purpose of a GO / NO GO plug gauge in thread gauging?
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How should an insert be positioned in the chamber when using a prewind tool?
How should an insert be positioned in the chamber when using a prewind tool?
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What action should be taken if the GO gauge indicates thread imperfections?
What action should be taken if the GO gauge indicates thread imperfections?
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What is essential to prevent distortion of an insert during installation?
What is essential to prevent distortion of an insert during installation?
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Where should the outer coil of the insert be installed in relation to the component surface?
Where should the outer coil of the insert be installed in relation to the component surface?
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Which tool is recommended for screwing an insert into a tapped hole?
Which tool is recommended for screwing an insert into a tapped hole?
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What should be avoided when transferring the insert from the tool into the tapped hole?
What should be avoided when transferring the insert from the tool into the tapped hole?
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What should be done with swarf and foreign matter on the thread after it has been cut?
What should be done with swarf and foreign matter on the thread after it has been cut?
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What effect does a shallow wedge angle have on friction in threaded fasteners?
What effect does a shallow wedge angle have on friction in threaded fasteners?
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What should be true about the tension force in threaded fasteners?
What should be true about the tension force in threaded fasteners?
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In the context of threaded fasteners, what are the two components involved?
In the context of threaded fasteners, what are the two components involved?
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What is the relationship between clamping force and compression load in female threads?
What is the relationship between clamping force and compression load in female threads?
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What is a desirable property of threaded fasteners, especially in smaller threads?
What is a desirable property of threaded fasteners, especially in smaller threads?
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How is the correct torque for preloading achieved?
How is the correct torque for preloading achieved?
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What happens to the strain and residual stress when the head of the bolt is no longer turned?
What happens to the strain and residual stress when the head of the bolt is no longer turned?
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What is the role of a coarse thread in producing motion?
What is the role of a coarse thread in producing motion?
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Study Notes
Fasteners
- Fasteners with screw threads allow parts to be fastened together, providing strength comparable to unthreaded fasteners. They can be disassembled and reassembled repeatedly.
- The helix, or Archimedes screw, was an early, practical thread type. The helix describes the path of a point traveling along the circumference of a circle while the circle advances along a line through its center.
- Pitch, in relation to a threaded fastener is the slope angle of the helical path per turn.
- An object traveling through a rotating helix experiences circumferential movement. The shortest distance between the feed and discharge ports is a straight line.
- The greater the pitch, the greater the axial advance per revolution, leading to a higher advance per turn. This may be advantageous, but higher axial advance also requires higher effort to turn the helix, and therefore, a lower helix pitch might be better for applications using muscle power.
General
- Basic wedge principle can be applied to creating a force multiplication. A steeper wedge increases the distance an object can be moved, though a shallower wedge can lift more weight.
Principle of a thread
- A wedge is a simple machine used to apply load.
- The distance an object will move depends on the inclination of the wedge (and the force applied).
- A steeper wedge will result in more movement but lift less weight. A shallower wedge will raise more weight but result in less movement.
Screw Threads
- Threads are either right or left-hand.
- Thread pitch (axial advance per turn) is usually expressed in threads-per-inch(TPI) or as an absolute dimension for one turn.
- Thread angle is important, for example, a 60-degree angle is common and used in UNF, UNC, ANF, ANC, or metric threaded fasteners.
- Thread types BA (47½°), BSW and BSF (55°), and Acme (29°) are examples of thread types with different angles.
Tolerances and classes of fit
- Thread classes (1-5) indicate varying tolerances.
- Class 1 is a loose fit; Class 2 is a free fit. Class 3 is medium; Class 4 is close; and Class 5 is a tight fit.
- Male (external) threads use an 'A' suffix, and female (internal) threads use a 'B' suffix; both parts must be the same class.
Bolts, Studs, and Screws
- Bolts and screws both have a head on one end with threads, but significantly differ in other aspects: a bolt has a relatively short threaded section and longer non-threaded grip; while a screw can have a long section of threading and no distinguishable grip length.
Bolts types
- Common bolt types include hex head bolts, 12-point head bolts, flush head bolts and screws.
- Socket head cap, or Allen screws, are available in most types of heads.
Screw nomenclature
- The major diameter is the measurement from crest to crest.
- The minor diameter is the measurement from root to root.
- The pitch diameter is the diameter of an imaginary cylinder passing through the threads.
Threads
- The lead or thread pitch (axial advance per turn) is often expressed in threads per inch (TPI) or as an absolute dimension.
- In most cases, the included thread angle is 60°.
Root, Flank, and Thread angle
- The root is the bottom of the thread.
- The flank is the surface of the thread that connects the crest to the root.
- The thread angle is the included angle between the flanks measured in the axial plane.
Lead
- The distance the screw thread advances in one complete turn.
Length of engagement
- The axial distance over which two mating threads engage.
Angular depth
- The vertical height of the triangle formed by the intersection of the extended flanks.
Actual depth
- The distance between the crest and root, measured perpendicular to the axis.
Fundamental triangle
- Formed by the intersection of the extended flanks of the thread.
Truncation
- The radial distance from the crest, or root, to the apex of the fundamental triangle.
Multiple threads
- Threads with two or more ridges.
Right-hand threads
- The thread is tightened when turned in a clockwise direction.
Left-hand threads
- The thread is tightened when turned in a counterclockwise direction.
Fine thread and coarse thread
- There is no difference in fatigue resistance between the two.
- Coarse threads are preferred when the female fastener is the weakest part.
Tolerances and classes of fit
- A, B, 1A, 1B, 2A, 2B, 3A, 3B define various fits, A and B referring to the male (external) and female (internal) thread components.
Screw nomenclature
- Major diameter: Distance between crests.
- Minor diameter: Distance between roots.
- Pitch diameter: Diameter of an imaginary cylinder passing through the threads.
Tolerances and classes of fit
- There are five classes of fit for Unified threads.
- A Class 1 is a loose fit; A Class 2 is a free fit; A Class 3 is a medium fit; a Class 4 is a close fit; and a Class 5 is a tight fit.
Locking devices
- Locking devices are used to prevent loosening or disengagement of mating components in various conditions.
- There are generally 1st class and 2nd class locking methods. First class includes wire locking, tab locking and split pinning. Second class refers to methods using friction, like spring washers or locking nuts.
Sheet spring nuts
- Used with standard and sheet metal self-tapping screws. These nuts provide a spring-loaded, arched section that prevents the screw from loosening.
- Commonly used in conduit, clamps or electrical equipment.
Instrument nuts
- Used to mount instruments on aircraft panels.
- Easily compressed to allow assembly and spring back to normal location without any fastening tools.
- Most are non-magnetic, often using brass or phosphor bronze.
Point-wrenching nuts
- Typically used for components needing high tensile length; easily tightened with a wrench.
- Relatively durable and suitable for high-stress applications.
Shear nuts
- Used with drilled clevis bolts and threaded taper pins.
- Normally exposed to shear stress only and are characterized by their castellated shape, or are drilled for wire locking or self-locking design.
Barrel nuts
- Used in high-stress applications requiring distributed load over the entirety of the metal.
- Typically are cylindrical with grooves to contain assembly and securely tighten without requiring additional support tools.
Thread inserts
- Used to maintain the original size of holes.
- They’re installed in the existing thread holes to provide greater resilience to mechanical thread wear.
Thin-wall inserts
- Used for thread holes in light alloy materials, such as aluminum, magnesium, bronze, etc.
- Designed to be extremely resilient, and not intended for high tension applications.
- They are commonly used in critical or demanding applications.
Key-locked inserts
- Their installation depends on accurate positioning with no twisting or distortion. The keys must be driven into place upon the correct installation.
- Used with a variety of types, materials and finishes.
Other types
- Anchor nuts are used for applications where a fixed or floating attachment to the structure is required.
- Clip nuts have a spring-steel clip housing designed for thin flanges.
- Clinch nuts have an unthreaded spigot that's swaged into the attachment hole in metal to hold them in position.
Nuts
- Most nuts are hexagonal.
- They're often the same size across flats as their corresponding bolt size.
- There are several types, including plain, shear, engine, drilled, slotted, and castellated.
- Some are intended for specific uses, like by-hex for use with an integrated washer. Others may be for quick release, as in wing nuts.
Stifnuts (Stiff nuts)
- Used to increase friction.
- They increase friction between the nut and its mating part.
- Several methods exist, like thread distortion (where part of the thread is distorted) or insert type (where a plastic or fiber insert is used within the thread).
Nyloc stiffnuts
- Using a nylon insert to achieve a high friction value.
- Designed for use only once.
Kayloc
- A light spring metal nut with an elliptical rear profile.
- Designed to maintain grip under twisting and movement.
Lightweight stiffnuts
- Similar to Kayloc, but in an oval shape.
- Provides locking by conforming to the round shape of the bolt.
Other locking devices
- Includes types like anchor, clip, and clinch nuts.
- Also includes instrument, and sheet spring types.
- These fasteners provide additional securement in various settings.
Aircraft rivets
- A rivet is a permanent fastening device, used extensively in aircraft construction for sheet metal and molded components.
- They typically are faster to install than screws, nuts, and bolts.
Solid rivets
- Usually are used for structural repair work.
- Also used for sheet metal work, and depend on their head type for classification.
- May also be used for the repair of various structural components.
Various types of head
- Includes types like snap, slug, countersunk, universal (AN470), flat, etc.
Specific rivets
- Avdel rivets come in various types, like snap head or countersunk.
- They are typically used in structural applications.
Hollow rivets
- There are two main classifications, open and blind rivets. Open rivets are closed by hammering using a punch while closed rivet use a mandrel to close them.
Pop rivets
- There are two types of pop rivets, break-stem, and break-head. Both require a specific tool for installation and are not usually reusable without damaging the rivet.
Other types
- Huck bolts are used with high-strength structural joints.
- This type has a pin and collar that use a swaging action to be placed into the structure.
Welding, Brazing and Soldering
- Soldering is joining two metals using a solder alloy and is commonly used in electronic applications.
- Brazing is joining two metals with a filler metal melted at a higher temperature than the parent metal.
- Welding is joining two metals using a filler metal at extremely high temperatures that causes them to melt.
- Fluxes are chemical compounds placed at the location where two metals are to be joined to prevent oxidation of the metals. Various types of flux are available.
- Different types of welding include manual metal arc welding, metal inert gas welding, tungsten inert gas welding, electron beam welding and flash butt welding, as well as resistance spot and seam welding.
Pipes and Hoses
- Pipes are structural components used to convey fluids and can be rigid or flexible.
- Hoses are flexible pipes, typically of rubber or synthetic materials, for conveying fluids among two or more components.
- Fittings are components to connect pipes.
- Flaring is a process for creating a flange on the end of a pipe for connecting to fittings.
- Flareless couplings involve a sleeve that's pressed into the pipe.
Control cables
- Used to operate various aircraft control surfaces, such as ailerons, elevators, and rudders.
- Several types are available, including cables with push-pull mechanisms.
- There are mechanisms which rely on pulleys and drums.
These are detailed, comprehensive study notes encompassing a variety of topics.
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Test your knowledge on fastening tools and various fasteners with this quiz. Explore questions about screwdrivers, spanners, and different types of nuts. It's a great way to assess your understanding of fastening techniques and their applications.
