Thread terminology, sectional views of threads. ISO Metric (Internal & External), BSW (Internal & External), Square and Acme, Sellers thread, American Standard thread.

1. Department of Mechanical Engineering
JSS Academy of Technical Education, Bangalore-560060
Computer Aided Machine Drawing
(Course Code:18ME46A)

2. TEXT BOOKS
• Machine Drawing, K R Gopala Krishna, Subhash Publication, 2005.
• Machine Drawing, N D Bhat & V M Panchal, Charoratar publishing house, 2005.
Further Reference:
 National Programme on Technology Enhanced Learning (NPTEL)
https://nptel.ac.in/courses/112103019/

3. • To impart knowledge of thread forms, fasteners, keys, joints and couplings.
Course Learning Objectives

4. Sheet No. 2
Thread terminology, sectional views of threads. ISO Metric (Internal & External),
BSW (Internal & External), Square and Acme, Sellers thread, American Standard
thread.

5. • Screw: A screw is a cylindrical rod, with a helical groove cut on it.
• Screw threads are used to fasten the parts together.
• Temporary fasteners
Sheet No.2 Thread Forms

6. Thread Terminology
Sheet No.2 Thread Forms

7. Thread form choice depends on;
• What it will be used for
• Length of engagement
• Load

8. Right-handed and left-handed threads
• The helix (or spiral) of a thread can be designed to be either right-handed or left-handed.
• Majority of threads are right-handed and follow the right-hand grip rule.
• Right-hand grip rule: When a thread is engaged in a connection, it moves upward if rotated in the direction
of the right hand.
• The letters “LH” in a thread spec stand for a left-handed thread.

9. Basic Profiles / Forms of Threads
Two basic profiles / forms of screw threads are;
1. V thread
2. Square thread

10. Standard forms of V Threads
1. Whitworth Thread – British Standard (BS) (55°)
2. Sellers thread - American Standard (60°)
3. ISO Thread (Unified Thread) – Indian Standard (60°)
1. Square Thread – Indian Standard
Standard forms of Square Threads
Modified forms of Square Threads
1. Acme Thread (29°)

11. Draw to scale 1:1, the standard profile of a BSW thread taking P = 50 mm. Show at least three
threads.
1. Whitworth Thread – British Standard (BS)
H = 0.96 P

12. Draw to scale 1:1, the standard profile of a Sellers thread taking P = 30 mm. Show at least three
threads.
2. Sellers Thread – American Standard
H = 0.86 P

13. Draw to scale 1:1, the standard profile of a ISO thread (both internal & external) taking P = 50
mm. Show at least three threads
3. ISO Thread – (Internal & External)
H = 0.86 P

14. Draw to scale 1:1, the standard profile of a ISO thread (both internal & external) taking P = 50
mm. Show at least three threads
3. ISO Thread – (Internal & External)
H = 0.86 P

15. Draw to scale 1:1, the standard profile of a Square thread, taking P = 50 mm. Show at least three
threads
4. Square Thread – (Internal & External)
H = 0.5 P

16. Draw to scale 1:1, the standard profile of a Acme thread, taking P = 50 mm. Show at least three
threads
5. Acme Thread – (Internal & External)
H = 0.5 P + 0.25 mm

17. End of Sheet No. 2