Threads And Fasteners Flashcards
What are the main purposes of a screw thread?
To transmit power and increase force
Control movement
Convey material
Hold parts together
Form a pressure tight joint
For measuring
What does pitch refer to?
Distance from a point on a screw thread to a corresponding point on the next thread. Measured parallel to its axis
What is major diameter
Largest diameter of screw head
What is minor diameter?
Smallest diameter of the thread
What is lead?
The distance a thread advances in one turn.
Single start screw lead is same as pitch
Two start screw the lead is twice the pitch
What is crest?
The top surface joining adjacent sides of the threads.
Can be flat, rounded, or sharp
What is root?
Root is the bottom surface joining to adjacent sides.
What is the flank?
Flank or side is the surface of the thread connecting the crest of the root.
What is thread angle?
Thread angle is is formed by the sides or flanks of a screw thread.
Most fasteners have a 60degree thread angle
When a thread winds clockwise and appears to be going away from you it is?
A right hand thread
What percent of load is taken by the first thread next to the washer and the second thread?
50 % for the first thread
25% for the second thread
The rest of the thread share the remaining 25%
What letter is internal thread?
B is internal thread
3/4”-10unc-2Ax1 1/2
3/4 = nominal diameter 10 = threads per inch UNC = thread style (unified national course 2= class of fit A = external thread 1 1/2 = length
What is a class 1 fit?
Maximum looseness
What is a class 2 fit?
An average fit.
Everyday nuts bolts and cap screws
What is class 3 fit?
No looseness in mating threads.
Cannot be assembled by hand.
What is a class 4 fit?
Precision threads
Usually used for precision tools and instruments such as micrometers.
What is a class 5/6 fit?
The most precise and accurate threads.
Used for extremely precise tools and high vibration conditions.
What are the four designations of ANT(American national thread)?
National course(Nc)
National fine (NF)
National extra fine (NEF)
National special (NS)
What are the 4 designations for unified screw thread?
Unified national course (UNC)
Unified national fine (UNF)
Unified national extra fine (UNEF)
Unified national special (UNS)
What is a constant pitch series?
Threads in this series have same pitch for all diameters
This series is a continuation of the extra fine thread series.
What is an acne thread used for?
Mainly used for an adjusting and positioning screw.
It has a 29degree included angle
What is the taper of a pipe thread?
3/4 inch per foot
M8x1.25x50mm means?
M = metric 8 = nominal size 1.25 = the pitch in mm 50mm = length