1. Trapezoidal threads are better than square threads as there is radial pressure or side thrust on the nut.
a) True
b) False
Explanation: Trapezoidal and not square threads suffer from the problem of bursting.
2. Trapezoidal threads screws have less load carrying capacity as compared to square thread screws.
a) True
b) False
Explanation: Square threads have less thickness at the core diameter and hence lower load carrying capacity.
3. Which of the following are true for buttress threads?
a) Combination of square and trapezoidal threads
b) Transmit motion in one direction only
c) They are used in vices
d) All of the mentioned
Explanation: As force is applied only in one direction in a vice so buttress threads are used.
4. Tr 40 x 14(P 7), here 14 indicates
a) Pitch
b) Lead
c) Diameter
d) None of the mentioned
Explanation: Tr=Trapezoidal threads,14=Lead(mm),7=Pitch(mm).
5. Nominal diameter of the screw thread is the same as core diameter.
a) True
b) False
Explanation: Nominal diameter is the largest diameter while core diameter is the smallest diameter of the screw thread.
6. If nominal diameter of screw thread=50mm and pitch=10mm then the mean diameter of the screw thread will be?
a) 40mm
b) 45mm
c) 60mm
d) 55mm
Explanation: Diameter(mean)=Diameter(nominal) – 0.5P .
7. If the load itself begin to the screw and descend down, unless a restraining torque is applied then the condition is termed as
a) Halting
b) Overhaulting
c) Front driving
d) None of the mentioned
Explanation: Overhaulting is the condition when load itsel begin to turn the screw.
8. Self-locking takes place when
a) Coefficient of friction is equal to or greater than the tangent of the helix angle
b) Coefficient of friction is lesser than or equal to the tangent of the helix angle
c) Coefficient of friction is equal to or greater than the tangent of the helix angle
d) None of the mentioned
Explanation: Self locking takes place if load does not descend on its own and that is possible only in c condition.
9. Efficiency of screw depends upon lead of the screw.
a) True
b) False
Explanation: Efficiency= WL/[Pπd].
10. Efficiency of the screw depends upon helix angle but does not depend on friction angle.
a) True
b) False
Explanation: Efficiency=tan(ἀ)/tan(Ǿ+ἀ) where ἀ=Helix angle and Ǿ=Friction angle.