Nylon and plastic tubing size is stated in terms of

• A. Tubing ID
• B. Tubing OD
• C. Wall thickness
• D. Color code

Answer: (B)

Sizing nylon and plastic tubing by outside diameter means the measurement you see on the tubing is the tube’s outer edge. Fittings and connectors are designed to seal against that external size, so using the outside diameter guarantees compatibility across different brands and parts. The inner diameter depends on the wall thickness, which can vary and isn’t standardized the same way, so relying on ID would make fitting compatibility unpredictable. Wall thickness is a secondary specification that affects flow and strength, not the labeling of tubing size. Color code is just a visual marker and doesn’t indicate the tube’s size.