Threads And Fasteners

Question 1

What are the main purposes of a screw thread?

Answer 1

To transmit power and increase force

Control movement

Convey material

Hold parts together

Form a pressure tight joint

For measuring

Question 2

What does pitch refer to?

Answer 2

Distance from a point on a screw thread to a corresponding point on the next thread. Measured parallel to its axis

Question 3

What is major diameter

Answer 3

Largest diameter of screw head

Question 4

What is minor diameter?

Answer 4

Smallest diameter of the thread

Question 5

What is lead?

Answer 5

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

Question 6

What is crest?

Answer 6

The top surface joining adjacent sides of the threads.

Can be flat, rounded, or sharp

Question 7

What is root?

Answer 7

Root is the bottom surface joining to adjacent sides.

Question 8

What is the flank?

Answer 8

Flank or side is the surface of the thread connecting the crest of the root.

Question 9

What is thread angle?

Answer 9

Thread angle is is formed by the sides or flanks of a screw thread.

Most fasteners have a 60degree thread angle

Question 10

When a thread winds clockwise and appears to be going away from you it is?

Answer 10

A right hand thread

Question 11

What percent of load is taken by the first thread next to the washer and the second thread?

Answer 11

50 % for the first thread

25% for the second thread

The rest of the thread share the remaining 25%

Question 12

What letter is internal thread?

Answer 12

B is internal thread

Question 13

3/4”-10unc-2Ax1 1/2

Answer 13

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

Question 14

What is a class 1 fit?

Answer 14

Maximum looseness

Question 15

What is a class 2 fit?

Answer 15

An average fit.

Everyday nuts bolts and cap screws

Question 16

What is class 3 fit?

Answer 16

No looseness in mating threads.

Cannot be assembled by hand.

Question 17

What is a class 4 fit?

Answer 17

Precision threads

Usually used for precision tools and instruments such as micrometers.

Question 18

What is a class 5/6 fit?

Answer 18

The most precise and accurate threads.

Used for extremely precise tools and high vibration conditions.

Question 19

What are the four designations of ANT(American national thread)?

Answer 19

National course(Nc)

National fine (NF)

National extra fine (NEF)

National special (NS)

Question 20

What are the 4 designations for unified screw thread?

Answer 20

Unified national course (UNC)

Unified national fine (UNF)

Unified national extra fine (UNEF)

Unified national special (UNS)

Question 21

What is a constant pitch series?

Answer 21

Threads in this series have same pitch for all diameters

This series is a continuation of the extra fine thread series.

Question 22

What is an acne thread used for?

Answer 22

Mainly used for an adjusting and positioning screw.

It has a 29degree included angle

Question 23

What is the taper of a pipe thread?

Answer 23

3/4 inch per foot

Question 24

M8x1.25x50mm means?

Answer 24

M = metric 
8 = nominal size 
1.25 = the pitch in mm
50mm = length

Question 25

What are the 3 ways fasteners are classified?

Answer 25

Tensile strength

Design or shape

Size and thread pitch

Question 26

A grade 5 bolt has how many lines?

Answer 26

3

Question 27

A grade 8 bolt has how many lines

Answer 27

5

Question 28

L9 bolts are high strength. How many lines do they have?

Answer 28

9

Question 29

A metric class 8.8 is comparable to what imperial bolt?

Answer 29

Grade 5 @ 830 mpa

Question 30

A metric class 10.9 is comparable to a what class imperial bolt?

Answer 30

Grade 8 @ 1040 mps

Question 31

A hexagonal nut is used for?

Answer 31

General purpose

Question 32

What are the slots for on a slotted hex nut?

Answer 32

To accept a cotter pin

Question 33

What is a stover nut and how does it work?

Answer 33

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

Question 34

What is a nylock

Answer 34

A self locking nut that uses nylon that applies pressure to the bolt.

Question 35

How do you find major diameter of a machine screw?

Answer 35

Multiply the screw number by .013 and add .060

Question 36

What are taper pins used for?

Answer 36

Taper pins are used to fasten machinery parts that need a precise fit.

Taper ratio is 1:48 (1/4” per foot)

Question 37

How does a spring pin work?

Answer 37

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

Question 38

What are the 3 types of convenience pins?

Answer 38

Spring locking pins

Straight leg pin

Quick lock pin

Question 39

Nominal diameter - pitch =‘s?

Answer 39

Tap drill size (TDS)

Question 40

What are the 3 ways fasteners fail during installations?

Answer 40

Shank may break

Strip external threads

Strip internal threads

Question 41

Tensile forces can be classed as?

Answer 41

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.