Understanding metric pipe thread sizes is essential for engineers, plumbers, and technicians working with fluid systems worldwide. These standardized dimensions ensure that components from different manufacturers fit together securely, preventing leaks and system failures. The metric pipe thread, often identified by the designation G, follows a thread form defined by ISO 7-1, featuring a 60-degree angle designed specifically for sealing without the need for a separate sealing compound in many applications.
Fundamentals of Metric Pipe Threads
Unlike tapered threads that rely on wedging action, parallel metric pipe threads rely on a specific gap known as the allowance gap at the crest and root of the thread to achieve a pressure-tight seal. This gap accommodates the elastic deformation of the sealing material, typically an O-ring or a soft filler, which is compressed between the male and female threads. The designation G, found on fittings and pipes, indicates a parallel (straight) thread form intended for pressure containment and pipe assembly, making it distinct from metric threads used for general fastening purposes.
Key Dimensions and Specifications The core of the metric pipe thread chart revolves around the nominal diameter, which corresponds to the approximate inner diameter of the pipe in millimeters. For example, a G1/2" thread has a nominal diameter of 12.7 mm. The chart below outlines the most common sizes, their corresponding approximate inner diameters, and the critical dimensions of the thread form, including the pitch and the major diameter. Nominal Size (G) Approx. Inner Diameter (mm) Pitch (mm) Major Diameter (mm) G1/4" 6.35 1.0 7.727 G1/2" 12.7 1.5 12.681 G3/4" 19.05 1.5 19.070 G1" 25.4 1.5 25.955 G11/4" 31.75 1.5 32.442 G11/2" 38.1 1.5 38.897 G2" 50.8 1.5 51.892 Practical Applications and Selection
The core of the metric pipe thread chart revolves around the nominal diameter, which corresponds to the approximate inner diameter of the pipe in millimeters. For example, a G1/2" thread has a nominal diameter of 12.7 mm. The chart below outlines the most common sizes, their corresponding approximate inner diameters, and the critical dimensions of the thread form, including the pitch and the major diameter.
Nominal Size (G) | Approx. Inner Diameter (mm) | Pitch (mm) | Major Diameter (mm)
G1/4" | 6.35 | 1.0 | 7.727
G1/2" | 12.7 | 1.5 | 12.681
G3/4" | 19.05 | 1.5 | 19.070
G1" | 25.4 | 1.5 | 25.955
G11/4" | 31.75 | 1.5 | 32.442
G11/2" | 38.1 | 1.5 | 38.897
G2" | 50.8 | 1.5 | 51.892
