6.5.1

Question 1

In thread forms, what are V threads normally used for?

Answer 1

Attaching parts

Aircraft nuts and bolts

Question 2

In thread forms, what is a buttress thread normally used for?

Answer 2

Takes Axial loads in one direction only

examply Bench vices

Question 3

What is the purpose of using multiple thread form?

Answer 3

Multiple threads are used to obtain an increase in lead without weakening the screw itself.

(Picture shows after 1 revolution)

Question 4

Thread pitch is described as being measured between?

Answer 4

The distance from the centre of one crest to the centre of the next crest measured parallel to the main axis.

Pitch is defined as the axial distance between adjacent threads on a helix or screw.

Question 5

Thread major diameter is described as being measured between?

Answer 5

The largest diameter of the thread measured in a plane normal to the axis.

Question 6

The lead in a screw thread is described as?

Answer 6

The lead for a screw thread is the axial travel for a single revolution

Example: double thread = 2

2 revolutions will procude 2 pitces

Question 7

Liner pitch on a screw thread is also called?

Answer 7

Lead

Question 8

What direction would right hand thread have to be turned to tighten a bolt?

Answer 8

Clockwise

Question 9

What type of thread has the ISO form?

Answer 9

Metric System

Question 10

Name the two series of ISO threads in common use?

Answer 10

Coarse Series for general use

Fine series for special applications

Question 11

What do the parts of the bolt number “1-8 UNC” mean?

Answer 11

1 = 1’’ Diameter Bolt

8 = 8 threads per inch

UNC thread - Unified Coarse

Question 12

What type of thread system is used on Boeing aircraft?

Answer 12

UNF - Unified Fine

Question 13

What type of gauges is used to ensure that threads meet the minimum metal limits
specified?

What 2 varieties do they come in?

Answer 13

Not Go Gauges

Come in low addendum or high addendum

Question 14

What type of gauge is used to ensure that threads meet the maximum metal limits
specified?

Answer 14

Go Gauge

Question 15

In thread forms, what is ACME threads normally used for?

Answer 15

ACME threads have flat roots and crests and are mostly used for motions of axial drives.

Examply: Trailing edge flap drive

Question 16

In thread forms, what are Round threads normally used for?

Answer 16

Used for motions of axial drive

especially stressed threads

Question 17

In thread forms, what are Ball Screw threads normally used for?

Answer 17

Used with re-circulating ball nuts

Aircraft flap drive and stabiliser drive units

Question 18

Thread minor diameter is described as being measured between?

Answer 18

The smallest diameter of the thread measured in a plane normal to the axis.

Question 19

Thread crest is described as being?

Answer 19

The crest is the top surface joining the flanks of the thread.

Question 20

Thread depth is described as being measured between?

Answer 20

The distance between the top of the crest and the bottom of an adjacent root. (both centre)

Question 21

What direction would left hand thread have to be turned to tighten a bolt?

Answer 21

Anti-clockwise

Question 22

Why are the roots of external threads always smoothly rounded?

Answer 22

To prevent cracking if the bolt is vibrating and threads are sharp would be hitting off structure.

Question 23

What are the main types of unified thread used for both ISO metric Threads and Unified inch threads?

Answer 23

UNF = Unified Fine

UNC = Unified Coarse

Question 24

What happens to threads below 1/4 inch diameter for both UNF and UNC?

Answer 24

Below 1/4 inch diameter the nominaal sizes of both are given as series of numbers from 0 to 12.

Question 25

In checking the minimum metal limit on threads, a No Go Gauge is used. What is the difference between the low addendum and high addendum varieties of the No Go Gauge?

Answer 25

A low addendum gauge only contacts the thread over a short length of flank ( Flank connects crest to root)

The high addendum guage has a much larger area of contact.

The low addendum is a better method for checking simple effective diameters while the high addendum is recommended for checking Unified threads in the numbered series.

Question 26

How is the minor diameter of an internal thread checked?

Answer 26

The minor diameter of the internal thread is checked with a plain Go plug gauge.

Question 27

What is the effective diameter tolerance?

Answer 27

Formula which takes into account the diameter, pitch and length of engagement

Also what is the depth/length of engagement?