For BSP Pipe Thread Fittings, ISO 228 (G) defines dimensions, tolerances and product grades. The sections below describe its scope, what it does NOT cover, and the equivalents across DIN, ISO and ASME.
ISO 228 (G) — Scope
ISO 228 (G) specifies the dimensions and tolerances of bsp pipe thread fittings. Material, property class, surface finish and packaging are governed by separate documents in the same standards family (for example ISO 898-1 for the mechanical property classes of bolts and screws).
Tolerance & Product Grades
ISO 228 (G), alongside the related ISO 228 (G) entries on this site, specifies product grades (typically A or B for fine work and C for general engineering) and tolerance classes for the controlling dimensions. Choose the grade against the precision your application requires.
Dimensions Specified by ISO 228 (G)
| Size | Nominal size (in) | Major diameter (mm) | Pitch (mm) | Threads per inch (TPI) | Tap drill (mm) | Reference standard | Notes |
|---|---|---|---|---|---|---|---|
| G1/16 | 1/16 | 7.723 | 0.907 | 28 | 6.8 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G1/8 | 1/8 | 9.728 | 0.907 | 28 | 8.8 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G1/4 | 1/4 | 13.157 | 1.337 | 19 | 11.5 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G3/8 | 3/8 | 16.662 | 1.337 | 19 | 15.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G1/2 | 1/2 | 20.955 | 1.814 | 14 | 18.5 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G5/8 | 5/8 | 22.911 | 1.814 | 14 | 20.5 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G3/4 | 3/4 | 26.441 | 1.814 | 14 | 24.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G7/8 | 7/8 | 30.201 | 1.814 | 14 | 27.5 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G1 | 1 | 33.249 | 2.309 | 11 | 30.5 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G1-1/8 | 1-1/8 | 37.897 | 2.309 | 11 | 35.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G1-1/4 | 1-1/4 | 41.91 | 2.309 | 11 | 39.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G1-1/2 | 1-1/2 | 47.803 | 2.309 | 11 | 45.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G1-3/4 | 1-3/4 | 53.746 | 2.309 | 11 | 51.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G2 | 2 | 59.614 | 2.309 | 11 | 57.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G2-1/4 | 2-1/4 | 65.71 | 2.309 | 11 | 63.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G2-1/2 | 2-1/2 | 75.184 | 2.309 | 11 | 72.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G2-3/4 | 2-3/4 | 81.534 | 2.309 | 11 | 79.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G3 | 3 | 87.884 | 2.309 | 11 | 85.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G3-1/2 | 3-1/2 | 100.33 | 2.309 | 11 | 97.5 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G4 | 4 | 113.03 | 2.309 | 11 | 110.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G5 | 5 | 138.43 | 2.309 | 11 | 135.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
| G6 | 6 | 163.83 | 2.309 | 11 | 160.0 | ISO 228-1 / DIN ISO 228 | Parallel pipe thread (G), sealed by gasket |
Equivalent Standards
Where direct equivalents exist (ISO ↔ DIN, ISO ↔ ASME), they are listed on the parent BSP Pipe Thread Fittings page. Always confirm against the dimensions on this page, since some "equivalent" standards differ in tolerances and head geometry.
When to Specify ISO 228 (G)
Choose ISO 228 (G) for international engineering work and OEM supply where ISO standards are the contractual reference. It is the default modern specification for bsp pipe thread fittings.