Page 129 - CITS - ED - Mechanical

ENGINEERING DRAWING - CITS

Vee threads

Types of `V' threads: The most commonly used thread before introducing metric thread is British Standard
Whit Worth thread (BSW), it is adopted by U.K. Fig 1 shows the proportions of the thread profile of BSW. Its
thread angle is 55°.
Pitch of a thread in inch system. P in inches = 1 divided by no.of threads in one inch.
Example: Designation 1/2" BSW i.e 1/2" nominal diameter, BSW thread, 12 TPI.
British Standard Fine (BSF) threads: Profile of the BSF thread is same as of BSW (55 ) but the pitches are
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finer comparing to pitches of same dia BSW threads. BSF threads are used in Automobile, Air crafts and for fine
mechanisms. Since the pitch is small, core dia or the effective dia is larger.
1
British Association thread (BA thread): Its angle is 47 2 .Designation example 1"BA - nominal dia 1" BA threads.
This thread is used, generally for small instruments. All the British Standard threads are of Inch system. (Fig 2)

Metric threads: IS:4218 Bureau of Indian Standards (BIS) has recommended the use of ISO metric threads. Its
thread angle is 60 . Fig 3a & b shows the metric thread form with proportions.
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Fig 1 Fig 2

Fig 3

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CITS :Engineering Drawing (Mechanical) - Exercise 8