This set of Engineering Metrology online quiz focuses on “Tolerance for Screw Thread Gauges and Screw Threads”.

1. How many variables are taken into consideration for the calculation of effective diameter tolerance?
a) 1
b) 2
c) 3
d) 4

Explanation: The screw threads combination is very much complex. There is a complicated interplay between pitch, thread angle and effective diameter. The effective diameter tolerance must take into consideration the three variables i.e. the major diameter, the length of thread engagement, the pitch.

2. What is the formula for tolerance on effective diameter (D = major diameter, L = length of engagement, p = pitch, a, b, c are constants)?
a) a∛D +b√L +c√p
b) a∜D +b√L +2c√p
c) a∛D +b√2L +c√p
d) 2a∛D +2b√L +3c√p

Explanation: Effective diameter tolerance depends on the Diameter, length of thread, pitch. It depends on them non linearly. Equation of tolerance is a∛D +b√L +c√p where D = major diameter, L = length of engagement, p = pitch, a, b, c are constants.

3. How the values of constants affect the accuracy of tools?
a) Decrease in accuracy will increase the value of constants
b) Increase in accuracy will increase the value of constants
c) Decrease in accuracy will reduce the value of constants
d) Increase in accuracy will reduce the value of constants

Explanation: The value of these constants will depend upon the prevailing accuracy of tools and machines used to produce the screw threads. Increase in accuracy will reduce the value of constants. The specifications provide for three grades of fits, (a) close, (b) medium, (c) free.

4. What are the values of constants for whit worth threads?
a) a=0.003 b=0.005, c=0.002
b) a=0.002, b=0.003, c=0.005
c) a=0.004, b=0.005, c=0.006
d) a=0.001, b=0.002, c=0.003

Explanation: The value of these constants according to British Standard Specifications for Whitworth threads for medium fit are a=0.002, b=0.003, c=0.005 i.e. the equation of tolerance on effective diameter is 0.002∛D +0.003√L +0.005√p

5. What is the relation between close fit and free fit?
a) Close fit tolerance is one third of free fit
b) Close fit tolerance is one half of free fit
c) Close fit tolerance is two thirds of free fit
d) Close fit tolerance is three fourths of free fit

Explanation: The basic formula gives effective diameter tolerance for medium fit. Close fit tolerances are two-thirds of free fit, and free fit tolerance is one and a half times that of medium fit. This results in tolerance increasing by 50% each time from close-medium-free fit.

6. Match the following fit with their use?(A- Fit, B-Usage)

A						B
1) Close		a) Suitable for bulk of screw threads
2) Medium	        b) Suitable for screw requiring fine snug fit
3) Free			c) Suitable for interchangeable screw threads

a) 1-a, 2-b, 3-c
b) 1-c, 2-b, 3-a
c) 1-b, 2-a, 3-c
d) 1-b, 2-c, 3-a

Explanation: Close fit applies to screw requiring a fine snug fit. Medium fit is suitable for better class of ordinary interchangeable screw threads and free fit is suitable for bulk of screw threads of ordinary commercial quality.

7. What is the major diameter tolerance of effective diameter for external threads?
a) +0.01√p
b) -0.05√p
c) +0.05√p
d) -0.01√p

Explanation: In major diameter, the tolerance is given by expression Effective Diameter tolerance = +0.01√p. It is applicable for all grades of fits for external threads. In major diameter, no such tolerance is laid down for internal threads.

8. What is the minor diameter tolerance of effective diameter for external threads?
a) Effective diameter tolerance+0.03√p & Effective diameter tolerance+0.01√p
b) Effective diameter tolerance+0.02√p & Effective diameter tolerance+0.01√p
c) Effective diameter tolerance+0.013√p & Effective diameter tolerance+0.02√p
d) Effective diameter tolerance+0.01√p & Effective diameter tolerance+0.02√p

Explanation: Minor diameter tolerance for external threads is (effective diameter tolerance + 0.013√p) for close fit and is ( effective diameter tolerance +0.02√p) for external threads in case of medium and free fit.

9. Which of the following is incorrect for the minor diameter tolerance of effective diameter for internal threads?
a) For 26 tpi : Tolerance = 0.2p+0.004”
b) For 26 tpi : Tolerance = 0.2p+0.005”
c) For 22 tpi : Tolerance = 0.2p+0.005”
d) For 26 tpi : Tolerance = 0.2p+0.007”

Explanation: For minor diameter tolerance of internal threads, tolerance for 26 tpi and finer is equal to 0.2p + 0.004”, tolerance for 24 tpi and 22 tpi is equal to 0.2p+0.004”, tolerance for 20 tpi and coarser is equal to 0.2p+0.004”.

10. Why Wide tolerance on core diameter of internal threads is given?
a) To prevent binding at the root of the tap
b) To prevent binding at the crest of the tap
c) To prevent binding at the flank of the tap
d) To prevent binding at the face of the tap

Explanation: To prevent binding at the root of the tap wide tolerance on the core diameter of internal threads is given. It permits a tapping drill being used of ample size. This follows a general practice and results in a flat crest to the root of the thread.

Sanfoundry Global Education & Learning Series – Engineering Metrology.

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