Steel fasteners – minimum tensile strength requirement for mild steel bolts and nuts For structural connections, the specified ultimate tensile strength of mild steel used for bolts and nuts should not be less than:

Introduction / Context:
In steel design, the material grade of bolts and nuts governs connection capacity. Traditional working-stress-method tables (in kg-based units) specify a minimum ultimate tensile strength for mild steel fasteners to ensure predictable shear and bearing behavior in riveted/bolted joints.

Given Data / Assumptions:

• Mild steel (MS) bolts and nuts used in structural steelwork.
• Question asks for the minimum ultimate tensile strength (not yield strength).
• Legacy units are kg/mm² consistent with classic Indian practice.

Concept / Approach:
Mild steel fasteners historically correspond to a minimum ultimate tensile strength near 400 MPa. Converting 400 MPa gives approximately 40 kg/mm², which is the commonly cited minimum for MS bolts/nuts in older tables.

Step-by-Step Solution:
Relate typical MS ultimate strength: 400 MPa ≈ 40 kg/mm².Select the nearest standardized minimum → 40 kg/mm².

Verification / Alternative check:
Modern property classes (e.g., 4.6) also imply an ultimate strength near 400 MPa, aligning with the 40 kg/mm² benchmark in legacy units.

Why Other Options Are Wrong:

• 32, 36 kg/mm²: too low for structural-grade MS fasteners.
• 44 kg/mm²: higher than the usual minimum for MS; aligns more with stronger grades.

Common Pitfalls:
Confusing yield strength with ultimate tensile strength; the question explicitly concerns tensile (ultimate) strength.

Final Answer:
40 kg/mm²