SIST EN 4120:2005

SIST EN 4120:2005 is the Slovenian adoption of EN 4120:2004 for aerospace self-locking bihexagonal nuts made from heat resisting nickel base alloy NI-PH1302 (Waspaloy), with silver plating on the thread. It specifies the nut characteristics, designation, marking and technical specification for parts in the 1 210 MPa / 730 °C classification.

What does SIST EN 4120:2005 specify?

SIST EN 4120:2005 specifies the characteristics of self-locking bihexagonal nuts in NI-PH1302, silver plated on thread, for aerospace applications. The document is organized into clauses on scope, normative references, required characteristics, designation, marking and technical specification.

Clause 3 contains the product definition in detail, including Figure 1 and Table 1 for the configuration, dimensions, tolerances, masses and thread codes. Clause 4 gives the designation format, Clause 5 covers marking, and Clause 6 points to the technical specification to be used with the nuts.

What are the key requirements of SIST EN 4120:2005?

SIST EN 4120:2005 ties the nut design to a specific geometry, material condition, surface treatment and identification method. In practice, this means a manufacturer, buyer or inspector can check the part against a single set of rules for form, finish and traceability.

Configuration, dimensions and mass

Clause 3.1 states that the configuration, dimensions, tolerances and masses are given in Figure 1 and Table 1. The dimensions and tolerances are in millimetres and apply after silver plating on the thread surface. For users, this is the main check for interchangeability and fit.

Thread form and size designation

Table 1 assigns thread codes to MJ thread sizes, and the thread limits are based on ISO 5855-2. This matters because the nut has to match the intended aerospace MJ bolt thread and the correct fit class.

Material condition

Clause 3.2 allows the nut material to be taken from EN 2959 or EN 3220. For procurement and quality control, this links the finished nut back to approved bar or wire product forms for forging or extrusion.

Surface treatment

Clause 3.3 requires electrolytic silver plating on the thread and chamfers in accordance with EN 2786. The thread area at MJ6 and above has a minimum thickness on the thread flanks, while MJ5 and the chamfers require complete coverage. In practice, the plating is part of the anti-seize and service performance of the fastener.

Form details and self-locking area

Figure 1 notes that the form of entry may be radius or chamfer within the stated limits, sharp edges are to be removed, and the self-locking zone may be intentionally out of round. That means the locking function is built into the geometry, so tooling and inspection have to respect the local form requirements.

Designation and marking

Clause 4 gives the designation format, using the standard number and thread code, with an optional I9005 code when needed. Clause 5 requires marking according to EN 2424, style A. This is what allows the part to be identified correctly in production, stock and maintenance.

Technical specification and class

Clause 6 points to EN 3005 for the technical specification. The classification 1 210 MPa / 730 °C links the nut to its strength level at ambient temperature and its maximum test temperature, which is the basis for selecting it in higher-temperature aerospace assemblies.

What terms does SIST EN 4120:2005 define?

Self-locking means the nut has a locking action built into its form so it resists loosening in service.

Bihexagonal means the nut has a 12-point wrenching configuration, matching the aerospace drive form used for the part.

NI-PH1302 (Waspaloy) is the heat resisting nickel base alloy specified for the nut material.

MJ thread is the aerospace metric thread form used for the threaded connection.

Silver plated on thread means the thread region is coated with electrolytic silver to meet the stated surface treatment requirement.

Classification 1 210 MPa / 730 °C identifies the strength and temperature class used to select the nut for service.

Who uses SIST EN 4120:2005?

SIST EN 4120:2005 is used by aerospace fastener manufacturers, suppliers of heat resisting alloy stock, design engineers, buyers, and quality inspectors. They use it to specify, make, check and buy self-locking nuts for aerospace assemblies where thread form, locking performance, plating and temperature class must match.

What changed in SIST EN 4120:2005 from the previous edition?

SIST EN 4120:2005 supersedes EN 4120:2003.

Which standards are used with SIST EN 4120:2005?

• ISO 4095 - gives the aerospace bihexagonal drive configuration used for wrenching the nut.
• ISO 5855-2 - gives the limit dimensions for MJ bolts and nuts.
• EN 2424 - sets the aerospace product marking style used in Clause 5.
• EN 2786 - specifies electrolytic silver plating of fasteners.
• EN 2959 - covers the heat resisting alloy NI-PH1302 bar condition used as a material option.
• EN 3220 - covers the NI-P101HT bar and wire condition used as a material option.
• EN 3005 - gives the technical specification for the same nut family and classification.

What does the SIST EN 4120:2005 document contain?

The document includes Figure 1 for the nut configuration and Table 1 for the thread code, associated dimensions and mass. Clause 3 also includes notes on entry form, edge finishing and the self-locking zone, which are useful for manufacture and inspection.

Clause 4 provides a designation example, including the standard number and thread code format. Clause 5 links marking to EN 2424 style A, and Clause 6 points to EN 3005 for the technical specification used with this nut family.