Unwin's Formula — Rivet Diameter vs Plate Thickness According to Unwin's empirical rule for riveted joints, the relation between the rivet (or rivet-hole) diameter d (in mm) and the plate thickness t (in mm) is best given by which of the following?

Introduction:
Unwin's formula is a classic empirical rule to select rivet diameter from plate thickness in traditional riveted construction.

Given Data / Assumptions:

• t in mm (plate thickness), d in mm (rivet or hole size, typically hole slightly larger than shank).
• Rule-of-thumb sizing, not a code-calibrated limit state design.

Concept / Approach:
Unwin's rule relates rivet diameter to the square root of the plate thickness, capturing the fact that rivet size grows sublinearly with thickness.

Step-by-Step Solution:
Unwin's recommended relation: d = 6 * sqrt(t)Example: for t = 9 mm, d ≈ 6 * 3 = 18 mm.Hole diameter is usually taken slightly larger than the rivet nominal diameter (e.g., +1 mm), but the core sizing follows this relation.

Verification / Alternative check:
Many classic design texts present d = 6 * sqrt(t) (with d and t in mm) as the selection guideline.

Why Other Options Are Wrong:

• Linear rules like d = t, 1.6 t, 2 t, or 6 t greatly over/under-size rivets across the thickness range and do not reflect Unwin's square-root dependence.

Common Pitfalls:
Confusing Unwin's formula with edge distance and pitch rules; they are separate detailing requirements.

Final Answer:
d = 6 * sqrt(t)