1. Threads-
Terminology in threads-
External thread-

2. Internal threads

3. Different Types of Thread profiles:-
Square Threads.
V-threads.
ACME Threads
Buttress Threads.
Whitworth threads
Thread Conventions

4. Square Threads
V- threads

5. ACME threads
Buttress threads

6. Whitworth Threads

7. STANDARD REPRESENTATION OF THREADS
Visible screw threads - For visible
screw threads, the crests of threads should be defined by a continuous thick line (type A), and the roots of threads by a continuous thin line (type B).
Hidden screw threads- For hidden screw threads, the crests and the roots should be defined by dashed lines.
Sections of threaded parts – For threaded parts shown in section, hatching should be extended to the line defining the crest of the thread.

8. End view of screw threads - On an end view of a visible screw thread, the thread roots should be represented by a portion of a circle, drawn with a continuous thin line (type B), of length approximately three-quarters of the circumference.
The above conventions apply to assemblies of threaded parts. However, externally threaded parts should always be shown covering internally threaded parts and should not hidden by them

9. METRIC THREAD STANDARDS

10. UNIFIED THREAD STANDARDS

11. Hexagonal headed bolt
Square headed bolt
Generally used when the head is to be accommodated in recess. Recess is also
made up of square shape to prevent rotation of bolt.
Square neck to avoid rotation of
Bolt while tightening a nut.

12. Cylindrical or cheese headed bolt
Used when-
Space for accommodating bolt head
is less.
Use of spanner is to be avoided.
Rotation of bolt is prevented by means of a pin
T- headed bolt
Primarily used in machine tool tables.
Fits in T slot provided on them.

13. Counter sunk headed bolt.
Used in application where head of
bolt must not project above the surface
of connected piece.
It may provided with the neck of square
cross-section.
Hook Bolt
This bolt passes through a hole of one piece
only. other piece is gripped by the hook shaped
bolt head.
This is used when it is not possible to drill hole
in the piece adjoining bolt head.

14. Eye Bolt-
Bolt has circular ring as its head.
Used as an appliance to lift heavy
machines.
Stud-
It consists of a cylindrical shank threaded
at both sides.
The nut end N is threaded for a length slightly
More than thickness of nut.
Metal end M is threaded to length at least equal
To diameter of stud.

15. Fitting of stud
Washer

16. Hexagonal nut
Approx Std. Dimensions
T=D; W=1.5D+3mm; R=1.4D
Rough Rule Dimensions
T=D; R=1.5D
Distance across diagonally opposite corners: 2D
Drawing a hexagonal nut

17. Nuts
Tommy Bar / Pin spanner

18. Locking arrangements for nuts
Due to vibrations, there is always a tendency to for nuts to get slack.
The nut A is first screwed on bolt as tightly as possible.
The nut B is then screwed on the bolt till it touches the top of nut A.
The nut B is help by spanner and nut A is turned backwards through few degrees.
The two nuts are hence locked tightly due to wedging action against each
other and bolt.
Nut B carries all the load, hence it is made thicker than nut A. Generally nut A
thickness is kept 0.8 times of thickness of nut B

21. Foundation bolts
Molten Lead / sulphur

22. Foundation bolts

23. Bolt type Picture Application Square headed Bearings of shaft
Cylindrical headed
Big end of connecting rods, eccentrics, etc.
T-headed
Machine tool tables, boiler mountings such as stop valve, feed check valve etc.
Counter-sunk headed
Where the bolt head must not project above surface
Eye bolt
For lifting heavy machines
Stud
Connect cylinder cover to engine cylinder
Situations where there is no space for bolt heads

24. END!!