Is the size of a flexible hose determined by its inside diameter or its outside diameter?

• A. Outside Diameter.
• B. Wall thickness.
• C. Both inside and outside.
• D. Inside Diameter.

Answer: (D)

The size of a flexible hose is defined by its inside diameter because the bore determines the flow area and what fittings it will mate with. The fluid passes through the internal channel, so the ID sets the capacity and compatibility with connectors. The outside diameter is influenced by wall thickness and construction and can vary even for hoses with the same ID, affecting strength and clearance but not the size designation. In practice, you choose by inside diameter, while the outer diameter matters for fit in the space and for clamps.