Thread Chart - Introduction

Fluid Port and Connector

Identification Guide

NPTF National Pipe Tapered Fuel
NPSM National Pipe Straight Mechanical
ISO International Standards Organization
SAE Society of Automotive Engineers
JIC Joint Industrial Council
NFPA National Fluid Power Association
BSP British Standard Pipe
DIN Deutsche Industrial Norme
JIS Japanese Industrial Standard
BSPT British Standard Pipe Tapered
BSPP British Standard Pipe Parallel


Because of their varied use in fluid piping systems, ports and connectors need to be correctly identified when adding or replacing hoses or tubes in your specific system.

A thread standard identifies the form, angle, diameter and pitch. ASME B1 .1 and ISO 261 are examples commonly used by thread manufacturers. The American Society of Manufacturing Engineers, American National Standards Institute, International Organization for Standardization, SAE International, British Association, and Deutsches Institut für Normung are a few of the organizations responsible for developing these standards.

Fluid Port and Connector Identification Tools:


Used to measure inner and outer thread diameters.

Thread Pitch Gauge:

Used to measure the number of threads per inch, as well as thread to thread spacing in the case of metric connections.

Before you begin measuring, be sure the threads are in good condition. Distorted or worn out threads can give you inaccurate measurements. Once you determine that the threads are in good condition, measure and note the diameter. (An I.D./O.D. caliper is a suitable tool for this.) Match the dimensions provided in this guide with your recorded measurements. You should be aware that due to manufacturing tolerances, your measurements may not specifically match those included in this guide.

You'll need to determine the spacing of the threads, per square inch (or thread to thread distances for metric connections), after measuring the diameter. It is important to be sure the thread pitch gauge properly fits on the threads to get the best accuracy. Note and compare your measurements with those in this guide.

For accurate measurement of four-bolt flanges, use a caliper to measure the port hole diameter of the bolt, and note that number. Then, measure the distance from center to center of the bolt holes, and note the longest spacing.

Dash Numbers:

The sizes of tubes and fluid pipes generally use an abbreviation called a dash number. When describing a fluid pipe or a tube using dash numbers, only the top number of the fraction is used. The bottom number is always 16 and is generally ignored. (Also, be aware that dash numbers are nominal.)

e.g. -8 size is equal to 8/16", or 1/2"

* Because metric measurements are actual sizes of a tube or a fluid pipe, dash numbers do not apply. For example, an M10x0.5 has threads on the outside of 10 mm with thread spacing of 0.5 mm.