# Engineering Drawing Questions and Answers – Definition and Forms Screw Threads

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This set of Engineering Drawing Multiple Choice Questions & Answers (MCQs) focuses on “Definition and Forms Screw Threads”.

1. A screw thread is often a _______ structure that aids in converting between rotational motion and linear motion.
a) Circular
b) Linear
c) Helical
d) Elliptical

Explanation: Screw Threads are designed by cutting helical grooves on a cylindrical surface, it is like a helical ridge wrapped around the cylindrical body which can convert between rotational motion and linear motion.

2. What is the largest diameter of the screw thread?
a) Core diameter
b) Pitch diameter
c) Nominal diameter
d) Helical diameter

Explanation: Nominal diameter or the major diameter of a screw thread is the largest diameter of the screw thread. It is an outer diameter of a screw which passes through the crests of external or the root of the internal thread.

3. What is the smallest diameter of the screw thread?
a) Pitch diameter
b) Core diameter
c) Nominal diameter
d) Helical diameter

Explanation: Core diameter is the smallest diameter of the screw, it passes through roots of the external diameter. Core diameter is also called a minor diameter of the screw.
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4. The mechanical advantage of the screw thread is __________ if D is the diameter of the screw, L is the distance between the threads.
a) D/L
b) L*D
c) πD/L
d) πD*L

Explanation: Mechanical advantage is defined as the ratio of the circumference of the screw to the pitch of the screw. When the diameter of the screw is D then the circumference of the screw is πD and the pitch or distance between the threads is L.

5. The axial distance advanced by the screw for one complete rotation is called ______
b) Pitch
c) Travel

Explanation: Lead of screw is the axial distance traveled by the screw when it completes one revolution, It majorly affects the mechanical advantage of the screw.

6. The diameter of the screw (D) is 20mm, the pitch of the screw (L) is 3mm. What is the mechanical advantage?
a) 21.1
b) 20.93
c) 22.9
d) 19

Explanation: Mechanical advantage (M.A.) of a screw thread is the ratio of the circumference of the screw(πD) to its pitch(L). Hence M.A. = $$\frac{\pi D}{L}$$. By calculating we get 20.933 as the mechanical advantage of the screw.

7. Which of the following is the conventional representation of External screw threads?
a) b) c) d) Explanation: For the simple representation of screw threads B.I.S recommended conventional representation of screw threads. Here the crest is represented by continuous thick line and roots by continuous thin line, from the side view, they are represented by circles, roots are represented by a portion of the circle.

8. Which of the following is the conventional representation of internal screw threads?
a) b) c) d) Explanation: For the internal threads, the root comes above the crests so the internal threads have a circular portion represented over the complete circle, as roots are represented by a portion of the circle.

9. Which of the following is true for single-start threads?

Explanation: In single-start threads for one complete turn of 360°, axial distance traveled will be equal to one pitch. Hence in-short lead is equal to pitch.

10. A screw thread designation is given by, M12 x 1.3. What does that indicate?
a) A marvelous thread of 12mm nominal diameter with 1.3 pitch
b) A metric thread of 12mm pitch with 1.3mm nominal diameter
c) A marvelous thread of 12mm pitch with 1.3mm nominal diameter
d) A metric thread of 12mm nominal diameter with 1.3 pitch

Explanation: Thread designation is done in the order of diameter-pitch. Type of screw thread is designated in the initial position. Hence, M= metric thread (I.S.O metric screw thread), 12mm is the nominal diameter and 1.3mm is the pitch.

11. Pitch diameter is the diameter of the imaginary circle passing through the points where the thread width is equal to ______
a) Pitch
d) approximately zero

Explanation: Pitch diameter is the diameter of an imaginary circle that passes through the points where thread width is equal to the distance between two threads that is the space between the two threads.

12. B.I.S recommends only fine threads.
a) True
b) False

Explanation: Coarse and fine are different size threads. Coarse threads have larger pitch whereas fine threads have a smaller pitch, hence these are two different thread series that B.I.S recommends.

13. What will be the basic triangle height for the screw thread profile of thread angle 60° and pitch 1.25?
a) 2.08
b) 1.08
c) 0.08
d) 3.08

Explanation: For the basic triangle height for the given screw thread profile is derived from the following figure From the figure, it is clear tan (30°) = (P/2)/H
Hence H = (√3/2)P.

14. A thread designation is given as M 8, what does that indicate?
a) A metric thread of fine pitch 1mm as 8mm is the nominal diameter
b) A metric thread of coarse pitch 1.25mm as 8mm is the nominal diameter
c) A metric thread of nominal diameter 8mm with pitch undefined
d) A metric thread of 8mm pitch with nominal diameter undefined

Explanation: According to thread designations, if the pitch is not indicated it means coarse pitch. From B.I.S diameter-pitch combinations for I.S.O metric threads, we can find the coarse pitch.

15. What is the relation between pitch and lead for double-start threads?

Explanation: In double-start threads, for one complete turn (360°) axial distance advanced by the nut is equal to twice of the pitch. Hence, lead = 2*pitch.

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