What Is the Dash on a Hydraulic Fitting?

By David Dunning; Updated April 24, 2017

In hydraulic systems, the dash number, dash size or simply dash is an industry standard measuring system for hoses and fittings. If you are replacing hoses or fittings, you should choose the correct dash size to avoid damage from heat or turbulence.

Hoses

The size of a hydraulic hose is described by its internal diameter, expressed as a dash number. The internal diameter of a hose measuring 1/4 of an inch can be divided into four segments, each measuring 1/16 of an inch, so the hose has a dash number of 4.

Fittings

Dash is used, along with other configuration codes, to provide meaningful shorthand descriptions of hydraulic parts. The dash is a single number that precedes the coupling description of a hydraulic part and denotes the fitting size in sixteenths of an inch.

Example

If a hydraulic adapter part is described as 6 MP – 4 FPX 90, the numbers 6 and 4 are dash numbers; this part has a 6/16 (3/8) of an inch male connector on one end and a 4/16 (1/4) female swivel connector on the other, at right angles (90 degrees) to each other.

About the Author

A full-time writer since 2006, David Dunning is a professional freelancer specializing in creative non-fiction. His work has appeared in "Golf Monthly," "Celtic Heritage," "Best of British" and numerous other magazines, as well as in the book "Defining Moments in History." Dunning has a Master of Science in computer science from the University of Kent.