Fasteners Flashcards
What is the form of a screw?
One complete contour between corresponding points on the crest
What is the crest of a screw?
The prominent point of the thread at the top
What is the root of a screw?
The bottom of the thread
What is the flank of a screw?
The slope between the root and crest
What is thread angle?
The angle between two adjacent flanks
What is the major diameter for a screw?
Male threads- diameter of the crest
Female threads- diameter of the root
What is the minor diameter of a screw?
Male thread- diameter of the root
Female thread- diameter of crest
What is the depth of a screw?
Radial distance between the root and crest
What is the pitch of a screw?
The distance between two crests or roots on the thread
What is the lead of a screw?
The distance covered in one rotation
What is the run out of a screw?
Where the minor diameter equals the major and merged into the plain shank
What are the the three old screw systems?
British association (BA) British standard (BS) American National (AN)
What are the three parts to BS screws?
BSW (whitworth)
BSF (fine)
BAP (pitch)
What is the max diameter and thread angle for BA screws?
1/4 diameter
47.5 degrees
What replaced the three screw systems?
The universal system
UNF fine
UNC coarse
UNEF extra fine
What is the thread angle for universal and American standards?
60
What is stronger in a hole, a fine or coarse screw?
Fine screw
What are the three types of transmission thread profiles?
Square
Buttress
Acme
Which thread type can only transmit power in one direction?
Buttress
Definition of a bolt?
Is tightened with a nut
Definition of a screw?
Tightened into a threaded hole by the head
If not stated, what is the minimum amount of the bolt or screw that should be extending through the nut?
1/32” including full chamfer
How is steel represented on a bolt?
X
What does a triangle symbolise on a bolt?
The material is of close tolerance
How is corrosion resistant steel indicated on a bolt?
Single dash
How is aluminium represented on a bolt?
Pair of dashes
What does the first of the last three digits represent in a bolt part number?
If it’s plated, or if the head or shank is drilled
What does the second last digit in a bolt part number represent?
The grip length in 1/16”
What does the last digit in a bolt part number represent?
How much over size it is
X- 1/64”
Y-1/32”
How long should the grip length of a bolt be?
Equal to the material thickness
How many washers can be used to adjust grip length?
Up to three maximum
What is a stud?
A piece of rod threaded at either end with a plain section in the middle
How can studs be fitted?
Lock nuts
Stud box
Stud insertion/removal tool
What is a stud box?
Hexagonal bar that’s drilled and tapped down the axial plain.
How is a stud box used?
One end is threaded halfway into the box and has a screw put in on the other side to lock it into one unit.
Then the stud is screwed in tightly using a spanner.
Which nuts are used for removal and insertion in the locknut method?
Insertion- top nut
Removal- bottom nut
How can damaged nuts be removed?
Filed flats
Ezi-outs
How does the field flats method of removal work?
Two sides of the stud are filed flat to allow an adjustable spanner to grip it easily and turn it out of the hole
How does an Ezi-out work?
A hole is drilled as large as possible into the nut, then the Eli-out tool is hammered in and used to twist the stud out
What are the three most common types of screws used in aircraft?
Machine screws
Structural screw
Self tapping screws
What materials can self tapping screws be used for?
Soft
What should self tapping screws never be used for?
Replacing standard screws and bolts in the original structure
What are the 4 types of nuts?
Non self locking
Locking nuts
High temperature self locking nuts
Low temperature self locking nuts
What are the 4 types of non self locking nuts?
Castle
Sheer castle
Slotted engine
Wing
What are the 5 types of locking nuts?
Locknut Nylock stiffnut Oddie Aero tight and phillidas Anchor nuts
When are high temperature nuts use and what material are they normally?
120C
CRES
What is the maximum temperature that low temperature self locking nuts can be used for and what are they made of?
121C
Fibres or nylon
What are heli-coil inserts?
Insets for softer metals to protect the threads in the holes
How much load does the heli-coil and first thread of a hole distribute?
Hole- 45-50%
Help-coil- full load distribution
What are the two types of help-coil?
Standard
Screw lock
How should holes be tapped is they are going to have a help-coil installed?
With a special tap provided by the manufacturer
What is the general rule with how deep help-coil should be in a hole?
Around 1/2 a pitch below the component surface.
How should the tang of a help-coil be removed in blind and through holes?
Blind hole- use long nose pliers and bend the tang back and forth till it fractures off
Through hole- use the inserting key or a special punch to punch it off with a sharp hammer blow
How can a hell-coil be removed?
By bending a new tang and using the insertion tool
By using a special extraction tool
What are the main locking devices used?
Wire locking Split pins Lock washer Locking plates Circlips Self locking nuts
How many twists per inch should there be when using locking wire?
8-10
What are the two methods of wire locking, and which more common?
Single twist
Double twist- most common
What are the three types of locking washers?
Tab washer
Spring washer
Shakeproof washer
Can split pins be reused?
Never
What quick release fasteners are used?
Pip pin- locating and locking Camloc Lightweight camloc Airloc Dzus
What is a camloc
A spring loaded assembly that locks into a grommet until the spring is compressed again.
What are lightweight camlocs used for?
Lightly loaded internal access pantelis
What are the 2 types of Dzus and where are they used?
Light duty- light fairings, box covers, light access panels
Heavy duty- cowlings and heavy fairings
What makes airlocs and Dzus similar?
They are both stud and receptacle fasteners
What are the two types of airloc?
Floating
Fixed
What is a key?
A piece of metal used to transmit a drive from a shaft to a hub
When are keys used?
When frequent separation is not required
What are the types of taper keys used?
Hollow saddle Flat saddle Gib headed Feather Woodruff
What are the 3 main material types used to make rivets?
Aluminium alloy
Monel
Titanium
What can affect the selection of a rivet?
The shear strength of the rivet in relation to the bearing strength of the material.
What is the general rule for choosing the size of a rivet?
Diameter should be 3 times the material thickness
What are the main aluminium alloys used in rivets, and how are they identified?
1100 (A) nothing on rivet 2117 (AD) dimple on rivet 2017 (D) raised dot on rivet 2024 (DD) pair of dashes on rivet 5056 (B) raised cross on rivet
What are the non aluminium alloy rivets and how are they identified?
CRS (F) no marking
Monel (M) two recessed dimples or raised R
Titanium (T) raised T or V
What are the two parts of a high lock or high lite?
Threaded pin with head
Collar with internal thread and external shear groove
How are high locks and high lites installed?
The hexagonal drive end of the collar used to hold it in place while the pin is screwed in to it until the torque that sheers off the hexagonal drive end of collar at the sheer groove
Can the plates being joined by threaded pin fasteners, does they have to be parallel?
No, the type of material will designate how much they can be misaligned
What type of fit are threaded pins used for?
Interference fit
What materials can high locks be made from?
Steel
CRS
Titanium
Should the lubrication on the threaded pins be removed?
Never
What should be checked before installing high locks and high lites?
Correct pin and collar (material, matching, etc.)
Correct grip length
If the pin has surface protection and lubrication
How much lighter are high lites compared to high locks?
Around 15%
What is a taper lok?
A tapered bolt with threaded end and self locking nut
When would a taper lok be used?
In areas that require high fatigue performance
