Riveted joints practice: If a hole of 25 mm diameter is drilled in plates for riveting, what should be the approximate diameter of the rivet shank (nominal rivet) for proper fit and driving?

Introduction / Context:
In structural and boiler riveting practice, the hole is made slightly larger than the rivet shank so the rivet can be inserted and then upset (formed) to fill the hole during driving. Choosing the correct clearance is a standard shop rule.

Given Data / Assumptions:

• Drilled hole diameter d_h = 25 mm.
• Conventional practice: hole diameter exceeds rivet nominal diameter by about 1.5 mm (typical workshop allowance).
• Goal: find nominal rivet diameter (shank size before driving).

Concept / Approach:
The usual clearance c between hole and rivet in hand or power riveting is about 1.0 to 1.5 mm (often 1.5 mm in many textbooks for up to about 25 mm rivets). Therefore, d_r ≈ d_h − c. The rivet expands plastically during upsetting to fill the hole tightly and ensure joint integrity.

Step-by-Step Solution:

Verification / Alternative check:
Typical workshop tables specify hole ≈ rivet + 1.5 mm for common sizes; field practice confirms this as a workable allowance.

Why Other Options Are Wrong:
23.0 mm: clearance 2.0 mm is excessive, risks poor fit.24.5 mm: clearance 0.5 mm may be too tight for consistent insertion and heating tolerances.25.0 mm: zero clearance; impractical for insertion before upset.

Common Pitfalls:
Confusing nominal rivet size with hole size; ignoring practical clearance needed for insertion and thermal expansion before closing the head.

Final Answer:

23.5 mm