Screw Threads + Nuts Flashcards
Form
Contour crest to crest
Crest
Top of thread, prominent point
Root
Bottom of thread groove
Flank
Slope from root to crest
Thread angle
Angle between flanks
Major diameter in male
Diameter from crest to crest
Major diameter in female
Diameter from root to root
Minor diameter in male
Diameter from root to root
Minor diameter in female
Diameter from crest to crest
Depth
Radial Distance from root to crest
Pitch
Distance from crest to crest
Lead
Distance advanced by the moving body of a mating pair in one complete rotation
Run-out
Where the minor diameter increases until it reaches major diameter (flank leading to plain part of screw)
British standard whitworth characteristics
Course, general purpose, 55 degree thread angle
British Standard Fine characteristics
- Finer than BSW
- Resists vibration
- Used on aircraft and vehicles
- 55 degree thread angle
British Standard Pipe characteristics
- Used in couplings
- Requires more material
- Have tapered crests
- 55 degree thread angle
British Associations characteristics
- Less than quarter inch diameter
- Scaled from 0-10 (10 =smallest)
- Used is small electrical parts
- 47.5 degree thread angle
American National Coarse characteristics
- Flat crest and root
- 60 degrees thread angle
American National Fine characteristics
- Finer than ANC
- 60 degree thread angle
What are the 3 categories of Unified thread forms and what are their thread angles?
- Unified National Course (UNC)
- Unified National Fine (UNF)
- Unified National Extra Fine (UNEF)
- All have a 60 degree thread angle
What tool is used to determine thread form
Screw pitch gauge/thread gauge
What 3 types of thread are used primarily as transmission threads. Used in screw jacks, lifting tackle and parts of heavy industrial machinery?
Square, Buttress and Acme
What is unique about Buttress threads?
Can only transmit power in one direction
Which type of thread is the most common?
Symmetrical V thread
Where does a screw tighten
Into a threaded hole
What does Chamfered mean?
A Lead has been filed into the thread
What must grip length equal when fitting a bolt
The thickness of the material
Where should bolts be identified from?
International Parts Catalogue (IPC)
What does the part number break down into?
Grip length, diameter, drillings and finish
What are bolts identified by other than part number?
Code marking
How many threads threads are permitted in the hole for materials thicker than 2.4mm?
2
How many threads are permitted in the hole for materials thinner than 2.4mm?
0
What is the maximum number of washers that can be used to alter grip length?
3
Why would you use a waisted stud?
It uses less material
Which stud provides the most rigidity?
Shouldered stud
What sort of material is a stepped stud used in and why?
Soft materials due to increased Anchorage
What 3 factors are studs categorised by?
- Tread type
- Diameter
- Overall length
What are the 3 methods of fitting a stud
- Stud box
- Stud insertion tool
- Lock nuts
What are the 3 methods of removing a stud?
- Lock nut
- Filing flats and using an appropriate spanner to remove
- Ezi-outs
What type of metal are self tapping screws used for?
Thin gauge sheet metal
What should self tapping screws not be used as?
Replacements for standard bolts and screws
What is used to lock down a castle nut?
A split pin
What is the difference between a castle nut as a shear castle nut?
Shear castle nut is used on areas with a lower tensile load
Which type of crenellated nut is designed for high temperature areas and is not approved for airframe use?
Slotted engine nut
Where are wing nuts used and why?
Frequently opened areas because they can be tightened and loosened by hand
What do plain nuts require to work?
Locking devices
What is a check nut used for?
As a locking device for plain nuts
What type of lock does a lock nut create?
Friction lock
What type of nut has an insert that will melt if used in a high temperature environment?
Nyloc stiff nut
How does an Oddie nut work?
6 springy tongues that are bent inward form a circle with a diameter less than the diameter of the root of the bolt thread, this grips the bolt thread in place
How do you tell the difference between an Aerotight and Philidas nut?
Aerotight has a vertical cut on the head, Philidas has a Horizontal cut on the head
What type of nut is fixed permanently in place?
Anchor nuts
Where are Anchor nuts used?
In areas you can’t get access to where screws need to be removed and refitted on a regular basis, such as panels
At what temperature are High temperature self locking nuts used?
120 degrees Celsius or higher
What is the maximum temperature at which Low temperature self locking nuts used?
121 degrees Celsius
What metal alloys are High temperature self locking nuts usually used with?
CRES, Steel alloy and silver plated CRES
What type of self locking nut has it’s threads out of phase?
High temperature self locking nuts
