For a standard flat-footed rail section used on Indian Broad Gauge, the typical width of the rail head (top portion) is approximately

Introduction / Context:
Rail head width is a key geometric parameter affecting wheel–rail contact, wear, permissible grinding profiles, and lateral strength. Standardized rail sections (e.g., 52 kg, 60 kg) have head dimensions within narrow ranges to ensure compatibility with rolling stock and maintenance equipment.

Given Data / Assumptions:

• Broad Gauge flat-footed rail sections as per common Indian standards.
• Question asks for the typical head width magnitude in millimetres.

Concept / Approach:

Representative head widths for prevalent sections fall around 66–68 mm. The value 66.77 mm is a standard rounded dimension used in many drawings and catalogues, reflecting the top running surface width excluding side fillets.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturers’ dimensional tables for common rail sections list head widths consistent with ≈ 66–68 mm; maintenance tooling and grinder templates match these values.

Why Other Options Are Wrong:

63.50 mm is undersized for standard heavy sections; 69.85 mm is larger than typical nominal; 136.52 mm corresponds to overall base dimensions, not head width; “None” is unnecessary.

Common Pitfalls:

Confusing head width with base width or overall rail height; assuming identical dimensions across all rail weights without checking sectional tables.

Final Answer:

66.77 mm