SIST EN 4118:2005

SIST EN 4118:2005 is the Slovenian adoption of EN 4118:2004 from SIST, for aerospace nuts made of heat resisting steel FE-PA2601 (A286) with silver plated threads. It specifies the characteristics, designation, marking and technical specification for self-locking bihexagonal nuts classified as 1 100 MPa at ambient temperature and 650 °C, so engineers and buyers can identify the exact nut type and the controlling requirements.

What does SIST EN 4118:2005 specify?

SIST EN 4118:2005 specifies self-locking bihexagonal nuts in FE-PA2601 (A286), silver plated on the thread, for aerospace applications. It organizes the subject into six clauses covering scope, normative references, required characteristics, designation, marking and technical specification, and it also includes Figure 1 and Table 1 for the nut geometry and sizes.

The scope is narrow and practical: it is about one nut family, one material, one surface condition and one aerospace classification. That helps a reader check quickly whether the standard matches the part they are sourcing, making, inspecting or certifying.

What are the key requirements of SIST EN 4118:2005?

SIST EN 4118:2005 ties the nut to a specific geometry, material, surface treatment and marking system. The most important requirements are in Clause 3, with Clause 4 to Clause 6 controlling how the part is identified and finished.

Geometry, dimensions and tolerances

Clause 3.1 points to Figure 1 and Table 1 for the configuration, dimensions, tolerances and masses. The dimensions and tolerances are given in millimetres and apply after silver plating on the thread surface.

In practice, this means the manufacturer has to control the final plated part, not only the machined blank. Buyers and inspectors should use the figure and table to verify the exact nut code, thread size and permitted form.

Materials

Clause 3.2 allows the nuts to be made from EN 2399 or EN 3639 material. That matters because the nut material must match the heat resisting and strength expectations of the standard.

Surface treatment

Clause 3.3 requires EN 2786 silver plating on the thread and chamfers. The thread treatment is not just decorative - it is part of the specified product condition.

The clause also distinguishes between thread sizes:

• For thread MJ6 and larger, the thread flanks need a minimum silver thickness.
• For thread MJ5, complete coverage is required.
• For chamfers, complete coverage is required.

For production and inspection, this means the plating process and coverage on critical surfaces are part of acceptance.

Form and functional details

Figure 1 and the notes under it control several functional details. They include removal of sharp edges, permissible forms of entry, the out-of-round condition in the self-locking zone, and the bihexagonal drive configuration in accordance with ISO 4095.

In practice, these notes tell the manufacturer where shape freedom is allowed and where it is not. They also show that some form variation is acceptable if the self-locking function is preserved.

Classification

The title classification 1 100 MPa at ambient temperature / 650 °C tells the user the performance class and the maximum test temperature. The notes explain that the first value relates to the minimum tensile stress the nut can withstand at ambient temperature without breaking or cracking when tested with a higher strength bolt.

That is important for selection, because the nut is not just defined by size - it is also defined by strength and temperature capability.

Designation, marking and technical specification

Clause 4 gives the designation format, including a thread code and an optional code I9005. Clause 5 requires marking in accordance with EN 2424, style A. Clause 6 points to EN 3004 for the technical specification.

For users, this means the nut must be ordered, identified and marked in a standard way, and the detailed technical rules are taken from the companion specification.

What terms does SIST EN 4118:2005 define?

The standard uses these key terms and abbreviations in its requirements:

• Bihexagonal - a 12-point drive form for the nut, used with the wrenching configuration in ISO 4095.
• Self-locking - a nut feature that resists loosening during service, especially important in vibration-prone aerospace assemblies.
• MJ thread - the aerospace metric thread form used for these nuts, with limits controlled by ISO 5855-2.
• FE-PA2601 (A286) - the heat resisting steel specified for the nuts.
• Silver plated on thread - the thread and chamfers receive electrolytic silver plating as required by EN 2786.
• EN 2424 - the marking standard used to identify aerospace products.
• EN 3004 - the technical specification that complements this nut standard.

Who uses SIST EN 4118:2005?

SIST EN 4118:2005 is used by aerospace manufacturers, fastener suppliers, inspectors and buyers who need a standard nut for aerospace assemblies. It is relevant when selecting materials, checking thread form and plating, writing procurement specifications or inspecting finished nuts against the required dimensions and marking.

What changed in SIST EN 4118:2005 from the previous edition?

SIST EN 4118:2005 replaces SIST EN 4118:2004. The European text it mirrors states that EN 4118:2004 supersedes EN 4118:2003.

Which standards are used with SIST EN 4118:2005?

• ISO 4095 - gives the bihexagonal drive and wrenching configuration.
• ISO 5855-2 - gives the limit dimensions for MJ bolts and nuts.
• EN 2399 - provides one permitted material source for the nuts.
• EN 2424 - specifies marking of aerospace products.
• EN 2786 - specifies electrolytic silver plating of fasteners.
• EN 3004 - gives the technical specification for this nut family.
• EN 3639 - provides another permitted material source for the nuts.

What does the SIST EN 4118:2005 document contain?

SIST EN 4118:2005 contains a dimensioned configuration drawing, a size table and a designation example. Figure 1 shows the nut form and key features, while Table 1 gives the thread codes, dimensional limits and approximate mass per 1 000 parts.

It also contains the marking reference to EN 2424, style A, and the technical specification reference to EN 3004. For users, that means the document is not only a definition of the nut type - it also tells them how to identify, finish and classify the part in procurement, production and inspection.