In turnout construction, what are stock rails and where are they fitted within the switch assembly?

Introduction / Context:
Turnouts enable a train to leave the main line to a diverging route. The switch assembly consists of stock rails and tongue (switch) rails that create the variable pathway. Understanding these components is fundamental to track design, maintenance, and safety inspections.

Given Data / Assumptions:

• Focus is on the identification and function of stock rails.
• Standard broad-gauge practice with conventional flat-footed rails.

Concept / Approach:

The stock rail is the running rail against which the tapered tongue rail fits tightly when the route is set. The stock rail provides a continuous guiding surface; the tongue rail moves to contact the stock rail on either side to select the route (main or diverging).

Step-by-Step Solution:

Verification / Alternative check:

Inspection manuals specify gauge and contact requirements between stock and tongue rails to avoid wheel-flange picking and ensure safe route selection.

Why Other Options Are Wrong:

(a) Crossing parts are separate assemblies; (b) check rails are used near crossings to control flange path, not in the switch contact; (d) stock rail extends beyond those limits; (e) expansion joints are different assemblies.

Common Pitfalls:

Confusing check-rail function with stock rail; assuming stock rails are interchangeable with common rails without specific planing for switch fit.

Final Answer:

Fitted against the tongue (switch) rails