IFI 128 Hex Coupling Nuts
IFI-128 is the Industrial Fasteners Institute standard specifically dedicated to hex coupling nuts. This standard provides complete dimensional requirements for inch-series coupling nuts ranging from nominal thread sizes 1/4″ through 6″. While IFI-128 has been partially integrated into ASME B18.2.2, it remains a recognized specification for coupling nuts in North American fastener markets.
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Product introduction
IFI-128 is the Industrial Fasteners Institute standard specifically dedicated to hex coupling nuts. This standard provides complete dimensional requirements for inch-series coupling nuts ranging from nominal thread sizes 1/4″ through 6″. While IFI-128 has been partially integrated into ASME B18.2.2, it remains a recognized specification for coupling nuts in North American fastener markets.
Common Specifications
| Materials | Carbon steel |
| Class | 2H |
| Range | 1/4″ – 6″ |
| Thread | Coarse , Fine, Extra Fine, Special-Fine |
| Surface | Plain, zinc plated, hot-dip galvanized, GEOMET, ZINC-NICKLE, DACROMATE etc. |
Key Features
- Dedicated standard for hex coupling nuts
- Inch thread series (UNC/UNF)
- Length typically 3 times nominal diameter
- Optional center inspection hole per IFI-128 Note 7
- Meets Industrial Fasteners Institute specifications
Application industry
- Structural steel tensioning systems
- Threaded rod extension assemblies
- Overhead crane and hoist installations
- Heavy equipment manufacturing
- Infrastructure and bridge construction
data table
| Size | 1/4 | 1/4 | 5/16 | 5/16 | 3/8 | 3/8 | 3/8 | 3/8 | 7/16 | 1/2 | 1/2 | 1/2 | 1/2 | 5/8 | 5/8 | 3/4 | 3/4 | 7/8 | 1 | 1 1/8 | 1 1/8 | 1 1/4 | 1 3/8 | 1 1/2 |
| UNC | 20 | 20 | 18 | 18 | 16 | 16 | 16 | 16 | 14 | 13 | 13 | 13 | 13 | 11 | 11 | 10 | 10 | 9 | 8 | 7 | 7 | 7 | 6 | 6 |
| s Min (inch) | 0.365 | 0.428 | 0.489 | 0.614 | 0.489 | 0.551 | 0.614 | 0.614 | 0.614 | 0.614 | 0.675 | 0.675 | 0.736 | 0.798 | 0.922 | 0.982 | 1.088 | 1.206 | 1.206 | 1.450 | 1.575 | 1.575 | 1.938 | 1.938 |
| s Max (inch) | 0.375 | 0.438 | 0.500 | 0.625 | 0.500 | 0.562 | 0.625 | 0.625 | 0.625 | 0.625 | 0.688 | 0.688 | 0.750 | 0.812 | 0.938 | 1.018 | 1.125 | 1.250 | 1.250 | 1.500 | 1.625 | 1.625 | 2.000 | 2.000 |
| e Min (inch) | 0.416 | 0.488 | 0.557 | 0.700 | 0.557 | 0.628 | 0.700 | 0.700 | 0.700 | 0.700 | 0.769 | 0.769 | 0.840 | 0.910 | 1.051 | 1.119 | 1.240 | 1.375 | 1.375 | 1.653 | 1.796 | 1.796 | 2.209 | 2.209 |
| e Max (inch) |
0.433 | 0.505 | 0.577 | 0.725 | 0.577 | 0.650 | 0.725 | 0.725 | 0.725 | 0.725 | 0.794 | 0.794 | 0.866 | 0.938 | 1.083 | 1.175 | 1.299 | 1.443 | 1.443 | 1.732 | 1.876 | 1.876 | 2.309 | 2.309 |
| m Min (inch) | 0.836 | 0.836 | 1.711 | 1.711 | 1.086 | 1.711 | 1.711 | 1.086 | 1.711 | 1.211 | 1.211 | 1.711 | 1.711 | 2.086 | 2.086 | 2.211 | 2.211 | 2.461 | 2.461 | 2.961 | 2.961 | 2.961 | 3.461 | 3.961 |
| m Max (inch) | 0.914 | 0.914 | 1.789 | 1.789 | 1.164 | 1.789 | 1.789 | 1.164 | 1.789 | 1.289 | 1.289 | 1.789 | 1.789 | 2.164 | 2.164 | 2.289 | 2.289 | 2.539 | 2.539 | 3.039 | 3.039 | 3.039 | 3.539 | 4.039 |
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