Summary:
- What is dash size?
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Dash size is the common method used to refer to the diameter of a hose or tube in 1/16″ increments.
For hoses this is a value for Inside Diameter, or I.D. For example, -6 hose would indicate a hose with inside diameter of 6/16″ – or 3/8″.
For tubes this is a value for Outside Diameter, or O.D. For example, a -10 tube would indicate a tube with an outside diameter of 10/16″ – or 5/8″.
By the way, dash sizes do not correspond to the exact hose inside dimension. Actual ID’s are smaller.
There are couple examples how to mark piping size at the schematic using dash size:
So, if you found at the drawing, for example, (-6) size, this means:
- For Hose: Internal Diameter is approx. 3/8″
- For Tube: Outside Diameter is 3/8″, therefore an Internal Diameter will be much smaller.
This is why sizes of tube and pipe have to be selected accurately, especially if you are going to connect them (for example, trough bulkhead fitting). Otherwise, you can get different flow rate and extra pressure drop in the line with smaller size.