1
Q
In what direction is a left-handed thread cut?
A
Anti-clockwise
2
Q
Define the ‘Form’ of a screw thread.
A
The shape of one complete contour of the thread between corresponding points on the thread crest along its length
3
Q
Define the ‘crest’ of a screw thread.
A
The prominent point of the thread, at the top of the thread
4
Q
Define the ‘Root’ of a screw thread.
A
The bottom point of the thread groove
5
Q
Define the ‘Flank’ of a screw thread.
A
The slope of thread between the root and crest
6
Q
Define the ‘Thread angle’ of a screw thread.
A
The angle between two adjacent flank slopes (where they meet at the root of the thread)
7
Q
Define the ‘Major diameter’ of a screw thread.
A
Diameter of the thread crest for male threads (aka crest diameter or normal diameter) and diameter of the thread root for female threads (essentially the biggest diameter available for the thread in question)
8
Q
Define the ‘Minor diameter’ of a screw thread.
A
The root diameter of a male threads and crest diameter of a female thread (essentially the smallest diameter available for the thread in question)
9
Q
Define the ‘Depth’ of a screw thread.
A
The radial distance between the root and crest of a thread
10
Q
Define the ‘Pitch’ of a screw thread.
A
Distance measured parallel to the screw axis between 2 corresponding points on the thread (eg crest to crest or root to root distance)
11
Q
Define the ‘Lead’ of a screw thread.
A
The distance the screw moves axially in one complete rotation (eg distance a screw moves into an anchor nut in one complete rotation)
12
Q
Define the ‘Run out’ of a screw thread.
A
The part of the thread where the minor diameter increases until it matches the major diameter and it meets the plain portion of the shank (ie the end of the threaded portion of a screw)
13
Q
Define the ‘Helix angle’ of a screw thread.
A
The axis of the bolt (slant of the threads when looked at from the side) measured in degrees
14
Q
What occurs if a nut is rotated onto the Run out of a thread?
A
It becomes thread bound
15
Q
What is the relationship between the lead of a single start thread, and its pitch?
A
Direct, they are the same
16
Q
Which has more holding power, single-lead threads or multiple-lead threads?
A
Single-lead threads, only single threads should be used where locking power is required
17
Q
What are 4 key advantages of Multiple-lead threads?
A
- They furnish more bearing area than single threads
- They have larger minor diameters giving the bolt stronger, better shear strength etc
- They provide rapid movement
- They are more efficient, losing less power to friction than single-lead threads
18
Q
What is the relationship between screw lead and Multiple-lead threads
A
The total screw lead is equal to the pitch multiplied by the number of leads (eg for a triple-lead thread the total lead is 3 times the pitch etc)
19
Q
What are the 3 most common thread standards used in aviation?
A
- British Standard Thread Forms
- American National Thread Forms (AN)
- Unified Thread Forms
20
Q
What are the 4 British Standard Thread Forms in general use?
A
- British Standard Whitworth (BSW)
- British Standard Fine (BSF)
- British Standard Pipe (BSP)
- British Association (BA)
21
Q
What are 4 characteristics of a British Standard Whitworth (BSW) thread?
A
- Coarse thread
- 55° thread angle
- Symmetrical V type thread
- Rounded equally at root and crest
22
Q
What are British Standard Whitworth (BSW) threads particularly suitable for?
A
Rapid assembly and disassembly of parts
23
Q
What are 2 advantages of British Standard Fine (BSF) threads?
A
- Finer adjustment available
- Better resistance to vibration
24
Q
What 2 factors make British Standard Pipe (BSP) thread well suited for pipeline couplings?
A
- Fine pitch ensures sufficient uncut material remains on the wall of the pipe meaning a stronger connection
- It may be tapered to ensure a pressure tight joint
25
What is the taper ratio on British Standard Pipe (BSP) thread?
1 in 16, based on the internal diameter of the pipe
26
What diameter are British Association (BA) threads used on?
Below 6.35mm (1/4 inch)
27
How are British Association (BA) threads expressed differently to other thread types?
Numerically, usually 1 to 10, larger number meaning smaller thread
28
What is the thread angle of a a British Association (BA) thread?
47.5°
29
What are the 2 American Standard Thread types?
1. American National Coarse (ANC)
2. American National Coarse Fine (ANF)
30
What are 2 characteristics of American National Coarse (ANC) threads?
1. Thread angle of 60°
2. Flattened crest and roots but not equal sized flats
31
What are 2 characteristics of American National Coarse Fine (ANF) threads?
1. Thread angle of 60°
2. Pointed roots and crests (no flats)
32
What are the 3 versions of Unified Thread Forms?
1. Unified National Coarse (UNC)
2. Unified National Fine (UNF)
3. Unified National Extra Fine (UNEF)
33
What are 2 characteristics of Unified National Thread Forms in general?
1. 60° Thread angle
2. Rounded roots and flat crests
34
What is the advantage of a coarse thread?
Greater lead (axial screw movement) for the same diameter than a fine thread
35
What are the 4 advantages of a fine pitched thread?
1. Stronger root portion
2. Greater hold
3. Finer adjustment
4. More resistant to shaking loose than a coarse pitch thread
36
What is the most common thread profile and why?
-Symmetrical V
-Combines strength with ease of engagement
37
What 3 things are Square thread profiles used for?
1. Lifting heavy loads
2. Transfer of Power
3. Exerting pressure
38
What thread profile is found on Screwjacks?
Square
39
What is the difference between Square and Acme thread profiles?
Acme is tapered
40
What is the Thread angle of Acme Threads?
29°
41
What is stronger, Square or Acme thread Profiles?
Acme
42
When are Buttress thread profiles used?
To handle heavy forces in one direction
43
Define the classes of fit from 1 to 5.
Class 1: Loose fit
Class 2: Free fit
Class 3: Medium fit
Class 4: Close fit
Class 5: Tight fit
44
What Class of fit are aircraft bolts usually manufactured in?
Class 3, medium fit
45
What Class of fit are aircraft screws usually manufactured in?
Class 2, Free fit
46
What is the difference between a bolt and screw generally?
A bolt is tightened with a nut, a Screw is tightened with its own head
47
Break down the Bolt ident code AN3-6A
AN = Airforce/Navy
3 = Diameter in sixteenths of an inch (3/16 inch)
6 = Length in eighths of an inch (6/8 inch long)
A = Not drilled for split pin (no letter would mean drilled)
48
What is the default bolt material?
Cadmium plated nickel steel
49
What is the ident for a corrosion resistant bolt
A letter C between the diameter and length numbers
e.g. AN3C6
50
What is the ident for Aluminium alloy bolts?
The letters DD inserted between the diameter and length numbers
e.g. AN3DD6
51
What is the physical bolt head marking for corrosion resistant steel?
A single dash
52
What is the physical bolt head marking for Aluminium?
2 raised dashes
53
What 2 bolts does the FAA forbid using in structures?
1. Aluminium alloy bolts
2. Steel alloy bolts smaller than AN3 (3/16 inch diameter)
54
What bolts does the FAA forbid using on frequently removed panels?
Aluminium alloy bolts
55
What 2 restrictions exist for using aluminium alloy nuts on cadmium plated steel bolts?
1. They must be loaded in shear
2. They must be on a land aircraft not a seaplane
56
What is used to identify if a bolt has a head drilled for lockwire?
A letter H after the diameter number
e.g. AN3H6A has a drilled head and an undrilled shank
57
When are Clevis bolts used?
When the load is applied in shear and free pivoting is required but not excessive play
e.g. control cable attach fittings
58
What 3 things are physically distinctive on a Clevis bolt?
1. It has a domed head, usually with a notch for a screwdriver
2. It has a small threaded portion of the shank relative to its length
3. It has a small notch between the threads and the shank
59
Break down the Clevis Bolt ident AN24-14A
AN = Airforce/Navy
2 = Clevis Bolt
4 = diameter in sixteenths of an inch (4/16 or 1/4 inch in this case)
14 = length in sixteenths of an inch (14/16 or 7/8 inch in this case)
A = not drilled for split pin
60
What is different in a Clevis bolt ident to that of a standard bolt?
The length is given in sixteenths of an inch instead of eighths of an inch due to it being more critical in Clevis bolts.
61
What is the AN range of Clevis bolts?
AN24 to AN36
62
What is the AN range of Eye bolts?
AN42 to AN49
63
Where are Eye bolts used?
Where external tension loads will be applied. E.g. attaching to turnbuckles to connect control cables
64
What is the AN range of drilled head engine bolts?
AN73 to AN81
65
How to AN73 to AN81 drilled head engine bolts physically differ from standard AN3 to AN20 bolts?
They have a thicker head with holes drilled through all flats and the centre of the head
66
What is the AN range of Close tolerance bolts?
AN173 to AN186
67
How to close tolerance bolts physically differ from standard bolts?
They have a triangle symbol on the head and are machined to a 0.0005 tolerance
68
Where are close tolerance bolts used?
Areas subject to pounding loads or in structure that will be riveted and bolted
69
Where are MS20004 to MS20024 Internal Wrenching bolts used?
In areas subjected to high tensile loads
70
What is required to provide a bearing area for an Internal Wrenching bolt installed in Aluminium alloy structure?
An MS20002C washer under the bolt head
71
What is visually distinctive on an Internal wrenching bolt?
They have an Allen key slot in the head and a radius between the head and shank that requires counterboring to accommodate it when installing on Steel parts
72
Why must an AN series bolt never be used to substitute an MS series Internal wrenching bolt?
The internal wrenching bolt has a much higher internal strength
73
Which type of bolts were developed and updated by National Aerospace Standards (NAS)?
Precision Airframe Bolts
74
What is the difference between even and odd dash numbers on a Precision Airframe Bolt ident?
-Even dash numbers are the standard length measurement in eighths of an inch
-Odd dash numbers are Special application bolts and measure length in sixteenths of an inch
75
Break down the NATO Standardisation Agency (NSA) bolt ident ‘NSA5022-6-18’
NSA5022 = NSA spec identifying bolt type
6 = Diameter in sixteenths of an inch (6/16 or 3/8 inch in this case)
18 = length in sixteenths of an inch (18/16 or 1 and 1/8 inches in this case)
76
What are the safety limits regarding bolt threads protruding from a self locking nut?
At least 1 thread must protrude but no more than 3
77
What does the dash number ‘-524’ represent for a self locking nut?
That it fits a 5/16 inch diameter fine thread bolt with 24 threads per inch
78
What is the temperature limit of Low temp, nylon self locking nuts?
They must not be used in any location where the temperature could exceed 121℃
79
What are the 2 restrictions that apply to AN364 nylon locking nuts and where are they designed to be used?
1. Only approved for shear loads
2. Not to be used under tension
-Designed to be used on undrilled Clevis bolts without split pins
80
What is the AN code for metal self locking nuts?
AN363
81
What are ganged anchor nuts?
Floating anchor nuts installed in a channel
82
Where are tinnerman nuts often used?
Light aircraft instrument panels
83
What 2 things are done to prevent interference when using Tinnerman nuts on instrument panels?
1. The nuts are made of brass
2. The cage holding the nut is made of phosphor bronze
84
What stops a rivnut spinning?
A key on the rivnut that aligns into a key way cut into the hole
85
Where is an AN310 standard castellated nut designed to fit?
Onto a standard class 3 (medium fit) bolt that will be subjected to either shear or tensile loads
86
What diameter is an AN310-6 nut designed to fit?
A 3/8 inch (6/16) diameter bolt
87
What is the difference between an AN320 shear castellated nut and an AN310 standard castellated nut?
The AN320 shear nut is thinner and only designed to be used on Clevis bolts
88
What type of nut is an AN315?
A plain nut with no castellations
89
How is an AN315 plain nut kept locked in place?
By using a spring washer that puts pressure on it and stops it shaking loose
90
Break down the nut identification AN315C-4L
AN315 = Plain nut with no
C = made of corrosion resistant steel
4 = fits a 1/4inch diameter bolt (4/16)
L = Has a left handed thread
91
What is an AN316 check nut?
A cadmium plated steel nut that is tightened onto an AN315 plain nut to ‘check’ it and keep it in place. It can be left or right handed thread just like the plain nut
92
Where are AN340 and AN345 light hex nuts used?
In non structural applications
93
What is an AN355 SLO Engine nut?
A castellated nut approved only for engine use, not airframe. Made of heat treated steel, with National fine threads that have a Class 3 medium fit
94
How does an AN360 Engine nut differ from an AN355?
It is a plain nut with no castellations and has a black rust proof finish
95
What 2 materials can wing nuts be made out of?
1. Cadmium plated steel
2. Brass
96
What fit do wing nuts have?
Class 2 (free fit)
97
What are the 3 basic classifications of screws used in aircraft construction?
1. Machine screws
2. Structural screws
3. Self-tapping screws
98
What is the difference between machine screws and bolts?
Screws have threads running along the full length of their shank, bolts have an unthreaded portion
99
What is the normal fit class for screws?
Class 2, free fit
100
What are the 4 most common types of screw?
1. Filister head
2. Flat head
3. Round head
4. Truss head
101
What do structural screws have the same shear strength as?
A bolt of the same size
102
What are structural screws made of?
Head treated steel alloys
103
What are the 2 most common flat head screw head angles?
1. 82 degrees
2. 100 degrees
104
How is a stud kept in place?
The short threaded end has a much coarser thread and tighter fit so the stud will stay in place when things are removed from the long threaded end
105
Why are studs used over bolts or screws?
To prevent tapped holes getting damaged at joins that need to be frequently separated
106
Where are waisted studs used?
Where strength must be retained but weight reduced
107
What is the advantage of stepped studs?
They provide a stronger anchorage than plain studs when being inserted into soft material
108
Where are shouldered studs used?
Where maximum rigidity is required against lateral stresses
109
What 3 methods can be used to insert and remove studs?
1. Stud box
2. Stud insertion tool
3. Lock nuts
110
What are the 2 types of Helicoil inserts?
1. Standard - provides a free running thread
2. Screw-lock - provides a resilient internal locking thread
111
How do helicoil inserts counter cross threading?
They can self adjust each thread to match the screw
112
What are self tapping screws used for?
Holding thin sheets of metal, plastic or plywood together
113
What’s the difference between type A and type B self tapping screws?
-Type A has a gimlet (sharp point)
-Type B has a blunt point and slightly finer threads
114
What are the 4 types of head available on self tapping screws?
1. Round head
2. Truss head
3. Countersunk flat head
4. Countersunk oval head
115
What is a Truss head?
A rounded screw head, similar to standard round heads but much thinner
116
What is the name given to a dowel rod that has been cut to size?
Dowel pin
117
What are the 4 types of dowel used on aircraft?
1. Smooth solid dowels
2. Hollow dowels
3. Threaded dowels
4. Split hollow dowels
118
Other than alignment, what are split hollow dowels used for?
They can act as a bushing for rotating components
119
What are the 3 commonly used lock washers in aviation?
1. Spring washer
2. Tab washer
3. Shakeproof washer
120
Is it permitted to reuse a tab washer?
No
121
Is it permitted to reuse a shakeproof washer?
Yes, as long as it maintains its springiness
122
What are the minimum twists per inch for lockwire?
6 to 8
123
What are locking plates made of?
Mild steel
124
Where are pal nuts ideally used?
In areas where frequent load changes would loosen regular nuts
125
What are pal nuts made of?
Light pressed alloy steel
126
What are 3 advantages of pal nuts?
1. Lightweight
2. Low profile
3. Vibration proof
127
What are the 3 most common types of quick release fasteners in aviation?
1. Dzus
2. Airloc
3. Camloc
128
What is the physical difference between light-duty and heavy-duty Dzus quick release fasteners?
The heavy-duty Dzus fasteners contain a grommet
129
What are the 2 types of available Airloc receptacles?
1. Fixed
2. Floating
130
How does a roll pin work?
It compresses when inserted, permitted by the cut out slot along its length, creating a spring action that holds it in place
131
What is the advantage of a Woodruff key?
Once it is in place, the part cannot move
132
What is required to use a square key?
A retaining device to hold it in place
133
What is the advantage of the Pratt and Whitney key?
Once it is in place, the part cannot move
134
What does the tang on a Gib head key do?
Governs insertion depth and allows removal
135
When does a GiB head key require retention?
In critical applications
136
What is the most used technique for joining aluminium?
Riveting
137
How far must a rivet extend from the base material before being driven?
At least 1.5x the rivet’s diameter
138
What diameter must a rivet’s formed bucktail be for it to be safe?
1.5x the rivet’s diameter
139
How far should a rivet’s formed bucktail extend from the base material to be considered safe?
0.5x the rivet’s diameter
140
Break down the rivet ident AN426AD4-6
AN = Airforce/Navy
426 = head style (countersunk)
AD = Alloy type
4 = Diameter in 1/32 (4/32 or 1/8 inch in this case)
6 = Length in 1/16 (6/16 or 3/8 inch in this case)
141
How is the length of a universal head AN470 rivet measured?
From the base of the head to the base of the shank
142
How is the length of a countersunk head AN426 rivet measured?
From the top of the head to the base of the shank
143
Why is the AN470 universal head rivet superior to other protruding head designs?
Improved fatigue strength and weight saving
144
Are protruding head or countersunk rivets generally stronger?
Protruding head rivers are stronger as no base material needs to be removed
145
What is Dimpling in regard to rivets?
Mechanically denting the surface of a material to accommodate the rivet head to improve aerodynamic smoothness
146
How far is it recommended to have a countersunk rivet head protruding before forming?
0.005 to 0.007 of an inch
147
Why should a countersunk rivet head protrude 0.005 to 0.007 of an inch before forming?
So the rivet gun can make full contact with it
148
What is are the 2 idents for 1100 Aluminium rivets?
1. A
2. Plain rivet
149
What is are the 2 idents for 2117 Aluminium alloy rivets?
1. AD
2. Dimpled rivet
150
What are the 2 idents for 5056 Aluminium alloy rivets?
1. B
2. Raised cross on rivet
151
What are the 2 idents for 2017 Aluminium alloy rivets?
1. D
2. Raised dot on rivet
152
What are the 2 idents for 2024 Aluminium alloy rivets?
1. DD
2. Two raised dashes on rivet
153
What are the 2 idents for 7050-T73 Aluminium alloy rivets?
1. E
2. Raised ring on rivet
154
What are the 2 idents for Corrosion resistant steel rivets?
1. F
2. No markings on rivet, shiny appearance
155
What are the 2 idents for Monel rivets?
1. M
2. Two dimples on rivet head
156
What is the ident for a Titanium rivet?
A raised V or T on the rivet
157
What is the advantage of cold driving 1100 (A) aluminium rivets?
The cold working increases their shear strength slightly
158
Where are 1100 (A) Aluminium rivets used?
Non structural applications
159
What is the main advantage of 2117-T3 aluminium alloy (AD) rivets?
High strength and shock resistance
160
Why are 5056 Aluminium alloy (B) rivets used in Magnesium structures?
They contain 5% magnesium so prevent dissimilar metal galvanic corrosion
161
Why are 2017 Aluminium alloy (D) rivets known as ‘ice-box’ rivets?
They are often frozen immediately after quenching to avoid them fully hardening so they can be worked
162
How many times can 2017 Aluminium alloy (D) rivets be reheated and reworked before losing structural strength?
Twice
163
Why did the aluminium industry modify 2017 Aluminium alloy (D) rivets?
To increase its minium shear strength to 234 Kiliopounds per square inch (KSI)
M6 Materials And Hardware
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