Bolt holes – standard clearance over nominal diameter For structural bolting, the diameter of a bolt hole is generally taken as the nominal bolt diameter plus:

Introduction / Context:
Standard bolt holes provide installation clearance. The hole diameter exceeds the nominal bolt diameter by a small allowance to accommodate fabrication tolerances and ease of erection.

Given Data / Assumptions:

• Common structural bolts and shop/site drilling practice.
• Standard holes (not oversized or slotted) are considered.

Concept / Approach:
Conventional practice uses a clearance of about 1.5 mm for standard holes in common bolt size ranges, ensuring fit-up without excessive slop that would compromise connection stiffness.

Step-by-Step Solution:
Hole diameter = nominal bolt diameter + clearance.Adopt clearance ≈ 1.5 mm → hole = d + 1.5 mm.

Verification / Alternative check:
Design standards list standard, oversize, and short/long slotted holes. The 1.5 mm increment corresponds to the “standard” category for many bolt sizes.

Why Other Options Are Wrong:

• 1.0–1.4 mm: may be insufficient for erection tolerance.
• 1.6 mm: close but not the conventional standard value.

Common Pitfalls:
Confusing standard holes with oversize or slotted holes, which use larger allowances and require special checks.

Final Answer:
1.5 mm