Question

Rahul found a bolt of $20 \times 2$, where 2 represents:

• A. Thickness of bolt
• B. Number of threads per mm
• C. Double start thread
• D. Distance between two corresponding points on the adjacent threads.
• A. Bolt
• B. Rivet
• C. Screw
• D. Stud
• A. Metric thread
• B. Mean diameter
• C. Major diameter
• D. Minor diameter
• A. Pitch
• B. Angle of thread
• C. Lead
• D. Flank

Answer 1

The Correct Option is D

Step 1: Decoding the Screw Thread Designation:
A standard thread designation on fasteners is written as $M \, d \times P$ (or simply $d \times P$):
• $M$ stands for ISO Metric Thread.
• $d$ represents the nominal (major) diameter of the thread in mm ($20\text{ mm}$ here).
• $P$ represents the pitch of the thread in mm ($2\text{ mm}$ here).

Step 2: Definition of Pitch:
By international mechanical standards, the pitch of a screw thread is defined as the distance measured parallel to the axis of the thread between a point on one thread and the corresponding point on the adjacent thread.

Step 3: Matching with Options:
Option (D) is the literal definition of thread pitch. Hence, option (D) is the correct answer.

Answer 2

Step 1: Classification of Fasteners:
Engineering fasteners are broadly classified into two categories based on their ease of disassembly:
• Temporary Fasteners: These allow assembly and disassembly of components multiple times without damaging either the fasteners or the joined parts (e.g., bolts, nuts, screws, studs, cotters, keys).
• Permanent Fasteners: These create joints that cannot be disassembled without destroying the fastener itself (and sometimes damaging the joined plates) (e.g., rivets, welds).

Step 2: Analyzing the Options:
Bolts (A), Screws (C), and Studs (D) are threaded, temporary fasteners. A Rivet (B) is a permanent mechanical fastener. To disassemble a riveted joint, the rivet head must be sheared off or drilled out.

Step 3: Conclusion:
Therefore, a rivet is not a temporary fastener, making option (B) correct.

Answer 3

Step 1: Understanding Standard Thread Designations:
Under the International Organization for Standardization (ISO) guidelines, screw threads are designated by a letter prefix followed by their nominal size (major diameter).

Step 2: Meaning of 'M':
The letter prefix 'M' specifies that the thread has an ISO Metric profile (a V-thread form with a $60^{\circ}$ included angle, standard crest truncation, and root rounding).

Step 3: Decoding the Numbers:
In M8, M10, and M12:
• 'M' = Metric Profile
• 8, 10, 12 = Nominal (major) diameter of the bolt in millimeters. Therefore, option (A) is correct.

Answer 4

Step 1: Distinguishing Pitch and Lead:
It is crucial to distinguish between the two primary helix parameters of a screw thread:
• Pitch ($P$): The distance between two adjacent thread crests.
• Lead ($L$): The linear axial distance a nut advances along the bolt for one full $360^{\circ}$ turn.

Step 2: Influence of Thread Starts ($n$):
The relationship between Lead and Pitch is governed by the number of independent helical threads wrapped around the cylinder (starts, $n$): $$L = n \times P$$
• For a single-start thread ($n=1$), Lead is equal to Pitch ($L = P$).
• For a double-start thread ($n=2$), Lead is twice the Pitch ($L = 2P$).

Step 3: Conclusion:
Since the physical distance advanced in one full turn is the definition of Lead, option (C) is correct.