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
What are the 3 ways fasteners are classified?
Tensile strength
Design or shape
Size and thread pitch
A grade 5 bolt has how many lines?
3
A grade 8 bolt has how many lines
5
L9 bolts are high strength. How many lines do they have?
9
A metric class 8.8 is comparable to what imperial bolt?
Grade 5 @ 830 mpa
A metric class 10.9 is comparable to a what class imperial bolt?
Grade 8 @ 1040 mps
A hexagonal nut is used for?
General purpose
What are the slots for on a slotted hex nut?
To accept a cotter pin
What is a stover nut and how does it work?
A stover nut is a self locking nut that have the top inner surfaces bent inward. When the top of the bolt is threaded onto the bolt it creates resistance
What is a nylock
A self locking nut that uses nylon that applies pressure to the bolt.
How do you find major diameter of a machine screw?
Multiply the screw number by .013 and add .060
What are taper pins used for?
Taper pins are used to fasten machinery parts that need a precise fit.
Taper ratio is 1:48 (1/4” per foot)
How does a spring pin work?
Spring pins are made slight larger with a slit cut into them. They depress when pushed into a hole and crest pressure against the hole
What are the 3 types of convenience pins?
Spring locking pins
Straight leg pin
Quick lock pin
Nominal diameter - pitch =‘s?
Tap drill size (TDS)
What are the 3 ways fasteners fail during installations?
Shank may break
Strip external threads
Strip internal threads
Tensile forces can be classed as?
Elastic limit - amount a fastener can stretched and still return to its original length
Yield point - where the fastener begins to take a permanent set.
Ultimate tensile strength - the failure or breaking point.
