This set of Engineering Metrology Multiple Choice Questions & Answers (MCQs) focuses on “Screw Thread Gauge Tolerance”.

1. How many types of tolerances are there in screw thread gauge tolerance?
a) 2
b) 3
c) 5
d) 4

Explanation: Tolerance for plug and ring screw gauges are covered in three classes, i.e. Reference, Inspection and workshop. Workshop gauges being within the work tolerance, and inspection and reference being outside.

2. What is the reference gauge tolerance for 6” diameter gauge?
a) 0.001”
b) 0.002”
c) 0.003”
d) 0.004”

Explanation: Tolerances were graded in terms of diameter. The workshop and inspection tolerance on gauges for 6” inches is 0.002” on effective diameter. Reference gauge tolerance was half of these tolerances i.e. 0.001” for 6”. This tolerance included the virtual effect of pitch and angle errors.

3. What is the tolerance on effective diameter for gauges upto 1.5” diameter as per B.S.S. No. 919?
a) 0.0002”
b) 0.0003”
c) 0.0004”
d) 0.0005”

Explanation: B.S.S. No. 919 was issued on screw gauge tolerance as an emergency. Specifications widened tolerance more on smaller size than larger. The tolerance was divided into two separate elements. For gauges upto 1.5″ diameter, Tolerance on effective diameter = 0.0004″.

4. What is the equivalent of pitch and angle tolerance on effective diameter for gauges upto 1.5” diameter as per B.S.S. No. 919?
a) 0.0004”
b) 0.0005”
c) 0.0006”
d) 0.0007”

Explanation: For gauges upto 1.5″ diameter, Equivalent of pitch and angle tolerance on effective diameter = 0.0005″. The simple effective diameter tolerance on NO GO gauge was same but virtual tolerance was halved. It is due to the fact that short length of thread is not liable to much pitch error.

5. What is the effect of pitch error upon the effective diameter of a screw thread?
a) D1 = E x K
b) D1 = 2E x K
c) D1 = E x K/2
d) D1 = E x K x 4

Explanation: The compensations for pitch and angle errors are also provided for by the application of corrections for each of these quantities. Effect of pitch error upon effective diameter of a screw thread is
D1 = E x K where D1=Effective dia. equivalent of pitch error, E = max. cumulative pitch error along the thread, K = constant for the shape of thread.
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6. A constant ‘K’ is used for defining the shape of thread. What is the value of ‘K’ for Whitworth?
a) 1.5
b) 1.62
c) 1.73
d) 1.92

Explanation: Effect of pitch error upon the effective diameter of a screw thread is D1 = E x K,
K = constant for the shape of thread = 1.92 for Whitworth, = 1.73 for International metric threads and = 2.27 for B.A.

7. What is the compensation for angle error?
a) ΔE=3p*ΔΘ/100
b) ΔE=p*ΔΘ/100
c) ΔE=p*ΔΘ/50
d) ΔE=p*ΔΘ/200

Explanation:The compensation for angle error, ΔE is related to the pitch p as follows: ΔE=p*Θ/100 where ΔΘ is the angle error in degrees. It is necessary that ΔE and p should be expressed in the same measure, i.e. English or metric. The angle error is the arithmetical sum of the errors of the two flank angles irrespective of their signs.

8. Which of the following item must fall within the prescribed limit for plug gauges?
a) Measured effective diameter along the pitch line
b) Measured effective diameter perpendicular to the pitch line
c) Measured minor diameter along the pitch line
d) Measured minor diameter perpendicular to the pitch line

Explanation: There are some requirements on effective dia which must be met before the gauge can be accepted i.e. the measured effective diameter along the pitch line and the measured effective diameter is +ΔE1+ΔE2 for plug gauges.

9. Which of the following item must fall within the prescribed limit for ring gauges?
a) Measured effective diameter +ΔE1+ΔE2
b) Measured effective diameter +ΔE1-ΔE2
c) Measured effective diameter -ΔE1-ΔE2
d) Measured effective diameter -ΔE1+ΔE2

Explanation: For ring gauges, requirements that must met are the measured effective diameter along the pitch line and the measured effective diameter -ΔE1-ΔE2. It should be noted that the max. allowable pitch error or the max. allowable angle error can readily be found from the formulae given, by evaluating ΔE1or ΔE2 to the full effective diameter tolerance allowed on any given size of gauge.

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