Dash Size Guide: What It Is and How to Interpret It in Plumbing Fittings

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What Does Dash Size Mean?

The “dash size” is a standardized designation system used to identify the sizes of pipes, fittings, and connectors in hydraulic and pneumatic systems. This system is based on a numerical notation that represents the outside diameter (OD) of the tube in imperial units.

How Does Dash Size Work?

  • Dash Notation (-): The dash size is indicated by a number preceded by a dash (e.g., -4, -8, -12). The number corresponds to the outside diameter of the tube expressed in 1/16 of an inch.
  • Conversion to Inches or Millimeters: To obtain the outside diameter in inches, divide the dash size number by 16. For example:
    • -4: 4 ÷ 16 = 1/4 inch (0.25 inches or approximately 6.35 mm).
    • -8: 8 ÷ 16 = 1/2 inch (0.5 inches or approximately 12.7 mm).
    • -12: 12 ÷ 16 = 3/4 inch (0.75 inches or approximately 19.05 mm).
  • Metric System Correlation: In some cases, the dash size can be approximately correlated with metric tube dimensions. However, remember that the dash size is always based on the outside diameter in inches.

Practical Example:

In the case of your product, the dash size is -12-12:

  • First “-12”: Indicates that the outside diameter of the tube connected to the first side (T1) is 3/4 inch (approximately 19.05 mm).
  • Second “-12”: Indicates that the outside diameter of the tube connected to the second side (T2) is also 3/4 inch.

Why Use Dash Size?

  • Standardization: Dash size is an international standard for hydraulic components, facilitating compatibility between tubes, fittings, and connectors from different manufacturers.
  • Simplicity: It’s a quick way to identify the size of a component without having to directly measure the outside diameter.
  • Specific Applications: Dash size is particularly useful in hydraulic systems, where dimensional precision is crucial to ensure sealing and performance.

Summary:

The dash size is a designation system that indicates the outside diameter of the tube in 1/16 of an inch. In your case, -12-12 means 3/4 inch (approximately 19.05 mm) for both sides of the fitting.