6.5 Flashcards
What is the definition of a screw thread?
The ridge left when a groove is cut into a cylindrical surface
What is the name for a thread if it is on the outside?
External or male thread
What is the name of a thread if it is inside the material?
Internal or female thread
When a thread is cut clockwise what is it called?
Right hand thread
What is a thread called if it is cut anti-clockwise?
Left hand thread
What is the crest of a thread?
The top point of the thread groove
What is the root of a thread?
The bottom of the thread
What is the flank of a thread?
The slope between root and crest
What is thread angle?
The angle between adjacent flanks
What is the major diameter of the thread?
The biggest diameter of the thread
What is the minor diameter of the thread?
The smallest diameter of the thread
What is the depth of a thread?
The radial distance between root and crest
What is the pitch of a thread?
Distance between crest-crest or root-root
What is the run-out of the thread?
The part where the minor diameter increases till it equals the major diameter
What is meant by multiple start threads?
When two or more start threads are cut side by side
What is lead of a thread?
The distance the thread has move in one complete rotation
What screw systems were used in Britain?
British standard (BS) and British association (BA)
Who designed the unified thread system?
International organisation for standardisation
What does BSW stand for in relation to fasteners?
British standard whitworth
What does BSF stand for in relation to fasteners?
British standard fine
What does BSP stand for in relation to fasteners?
British standard pipe
When is British standard whitworth BSW used?
For general purpose work in metal and plastics
When is British standard fine BSF used?
Anywhere with high vibration due to its smaller thread
When is British standard pipe BSP used?
When working on pipeline couplings
What are the three types of unified thread?
UNC- unified national coarse
UNF- unified national fine
UNEF- unified national extra fine
What is the thread angle of a British standard whitworth?
55°
What is the thread angle of a British association?
47.5°
What angle is used in American threads?
60°
What is the thread angle in the unified thread system?
60°
What is meant by a thread having a coarse pitch?
It has a greater lead (deeper but less threads)
What is meant by a thread having a fine pitch?
It has a smaller lead (more but shallow threads)
Why is having a fine pitch thread better than a coarse pitch?
- stronger root
- finer adjustment
- higher vibration resistance
What is a screw pitch gauge?
A gauge that allows you to quickly know the thread pitch
When are the square, buttress, acme threads used?
When transmission is needed such as lifting or screw jacks
What is special about the buttress thread type?
It can only transmit power in one direction
