Threads

Threads are applied for interconnection of machine parts and for transmitting motion from one part to another. When a thread is cut on the outside of a part it is known as an external or "male thread". A thread is callad an "internal" or "female thread" When cut inside a part. Depending on the shape of the threading tool different profiles of thread are obtained, such as triangular, square, or trapezoidal.

In practice triangular threads are most widely used. The main elements of a thread are: the angle of the thread, the major, minor and pitch diameters, the depth and the pitch.

Screw threafds are of both right-hand and left-hand types. In right-hand threads the direction of the thread is from the right to the left. Right-hand thread screws are turned clockwise to be screwed into a nut, while left-handed screws should be turned counterclockwise to do that. In screw fastenings threads are made of various shapes, but always of the triangular type: such as: single thread, double thread and triple thread. On the type of the latter depends the lead of the thread which is the distance a screw thread advances axially in in one turn. On a single thread screw the lead and the pitch are the same; on the double thread screw the lead is twice the pitch, while on a triple thread screw the lead is three times the pitch.

The most widely used systems of triangular threads in machine-building are: metric, inch and pipe threads, Each thread has its own angle and application. A metric thread profile resembles a triangle with an angle of 60° at its apex. Such a thread is widely used for bolts and nuts. An inch thread profile has an angle of 55°. This type of thread may be used when making spare parts for foreign-made machines. An angle of 55° is also used with pipe threads. Pipe threads are applied for gas and water pipes, as well as for clutches connecting such pipes.

ІІІ. Language

Ex.7. Match word and word combinations in column A with those in column B:

Column A	Column B
thread shape depend on screw nut clockwise counterclockwise spare parts fastening pitch	гвинт кріплення форма запасні частини поступ гайка різьба залежати від за годинною стрілкою проти годинникової стрілки

Ex.8. Find in the text nouns for these verbs:

To move, to part, to screw, to direct, to faster, to turn, to lead , to apply, to connect.

Ex. 9. Fill in the blanks using the following words:

a) depending on, b) turn, c) nuts, d) triangular thread, e) clutches, f) spare parts,

g)pipe thread, h) external thread.

1. When a thread is cut on the outside of a part it is known as an ………. .

2. …… the shape of the thread tool different profiles of thread are obtained.

3. In practice ………. are most widely used.

4. On the type of the thread depends …………… of the thread .

5. The most widely used system of triangular thread in machine-building are: metric, inch and …………. .

6. A metric thread profile is widely used for bolts and ………….. .

7. An inch thread profile may be used when making ……………. For foreign-made machines.

8. Pipe threads are applied for gas and water pipes and for ………….. connecting such pipes.

Ex.10. Match the beginning of the sentence in column A with the ending in column B:

Column A	Column B
Threads are applied A thread is called internal The main elements of a thread are In right-hand thread Depending on the shape of the threading tool	the direction of the thread is from the right to the left. different profiles of thread are obtained, such as: triangular, square or trapezoidal. for interconnection of machine parts and for transmitting motion from one part to another. when cut inside a part. the angle of the thread, the major, minor and pitch diameters the depth and the pitch.

ІV. Comprehension

Ex. 11. Agree or disagree with the following statements:

1. Threads are applied for interconnection of machine parts .

2. A thread is called an “ internal ” or “ female thread” when cut inside a part.

3. In practice square threads are most widely used.

4. Screw threads are of both right-hand and left-hand types.

5. Left-hand thread screws are turned clockwise to be screwed into a nut.

6. Each thread has its own angle and application.

7. A metric thread profile resembles a triangle with an angle of 60 at its apex.

8. An inch thread profile has an angle of 55.

Ex. 12. Answer the questions:

1. What are treads used for?

2. What types of threads do you know?

3. What are the main elements of a thread?

4. What types of screw threads do you know?

5. What are the most widely used systems of triangular threads in machine-building?