Understanding Dash Sizing: A Guide to Properly Sizing Hydraulic Hoses

When it comes to hydraulic hose fittings, it’s important to get the correct size to prevent issues such as leaks or flow restrictions and to ensure optimal performance while protecting your equipment. In the hydraulics world, the dash size, sometimes referred to as dash number or dash, is an industry standard measuring system for hoses and fittings. The dash sizing system is one of most common misunderstandings when ordering hydraulic fittings. Simply put, a dash size refers to the inside diameter of a hose, tube, or fitting in 1/16” increments.

For example, if the size of a hydraulic fitting is -8AN, sometimes written as -08, the fitting is 8/16ths of an inch. Simplified down, the size of the hole is 1/2”. With the inside diameter being 1/2”, the threads of the fitting need to be larger to ensure a snug, but not too tight, fit. Following the chart below, the external threads of an -8AN fitting is 3/4”-16 UNF (Unified Fine Pitch). These dimensions often get mixed up resulting in the wrong fitting size being ordered.

The AN Thread Sizes chart to the right will help clarify the dash sizing system.

1. Using a caliper, measure the inside diameter of the hole going through the fitting.

2. Using a thread pitch gauge, find the  thread pitch of the outside of the fitting.