Question

Select the correct option regarding plain washer.
(i) A circular plate having a square hole in its centre.
(ii) The standard inner diameter is ‘d + 1’.
(iii) Its outer diameter is ‘2d’.
(iv) It is placed below the nut.

• A. (i) and (ii) only
• B. (ii) and (iii) only
• C. (ii) and (iv) only
• D. (iii) and (iv) only

Hint:

Standard plain washer formulas for drawing:
• Inner Hole Diameter ($d_i$) = $d + 1$ mm
• Outer Diameter ($D$) = $2d + 3$ mm
• Thickness ($t$) = $0.15d$

Answer 1

The Correct Option is C

Step 1: Evaluating Statement (i):
“A circular plate having a square hole in its centre.”
A plain washer is a thin, flat circular annulus (ring) containing a circular hole in its center to accommodate the threaded cylindrical shank of a bolt. It does not have a square hole. Thus, statement (i) is incorrect.

Step 2: Evaluating Statement (ii):
“The standard inner diameter is $d + 1$.”
The inner hole diameter of a plain washer must be slightly larger than the nominal bolt diameter $d$ to allow free passage of the bolt. In standard engineering graphics drawing conventions, the inner diameter of the washer is taken as $d + 1$ mm (or $d + 1.5$ mm). Thus, statement (ii) is correct.

Step 3: Evaluating Statement (iii):
“Its outer diameter is $2d$.”
According to BIS standards, the actual formula used to draw a standard plain washer's outer diameter is $2d + 3$ mm. Although $2d$ is sometimes used as a rough approximation, the strict proportion is $2d + 3$ mm. Let us hold this and check statement (iv).

Step 4: Evaluating Statement (iv):
“It is placed below the nut.”
A washer is placed beneath the nut to distribute the clamping pressure over a wider area, prevent damage to the surface of the clamped parts, and prevent loosening. Thus, statement (iv) is absolutely correct.

Step 5: Selecting the Best Combined Option:
Since (ii) and (iv) are both highly accurate and correct, the option corresponding to this pair is (C).