SIST EN 3725:2005

SIST EN 3725:2005 is the Slovenian adoption of EN 3725:2004 from CEN for aerospace pan head screws with a six lobe recess, normal shank and long thread, made in titanium alloy TI-P64001, anodized and MoS2 coated. It specifies the screw characteristics, designation, marking and technical specifications for use in aerospace applications, so designers, manufacturers, inspectors and buyers can identify the exact fastener type they need.

What does SIST EN 3725:2005 specify?

SIST EN 3725:2005 specifies the characteristics of pan head screws with six lobe recess, threaded to head, in TI-P64001, anodized and MoS2 coated, for aerospace applications. The document is organized into a foreword, clauses 1 to 6, one figure and three tables.

• Clause 1 states the scope and the strength class.
• Clause 2 lists the normative references needed to apply the standard.
• Clause 3 gives the required characteristics, including configuration, materials and surface treatment.
• Clause 4 defines the designation system.
• Clause 5 covers marking.
• Clause 6 points to the technical specifications that apply.

What are the key requirements of SIST EN 3725:2005?

SIST EN 3725:2005 defines the product form, the material and coating, the way the screw is designated, and the references that control its recess and technical details. In practice, that means the standard is used to order, make, inspect and identify one specific aerospace screw family.

• Scope and strength class - The screws are specified at a strength class of 1 100 MPa at ambient temperature. The note adds that, because of the recess geometry, the strength class used for seating torque calculation shall not be greater than 900 MPa. This matters when setting tightening data and avoiding overloading the recess.
• Configuration, dimensions and masses - Clause 3.1 refers to Figure 1 and Tables 1 and 2 for the screw shape, dimensions, tolerances and masses. The dimensions and tolerances apply after anodizing but before MoS coating, which matters for inspection and acceptance.
• Thread and recess definition - Figure 1 and Table 1 tie the screw to MJ thread codes and to the six lobe recess defined by EN 3911. This gives the manufacturer and inspector a common reference for thread form and drive geometry.
• Material - Clause 3.2 specifies EN 3813. For users, this means the material condition is not chosen ad hoc - it is linked to the titanium alloy standard named by the document.
• Surface treatment - Clause 3.3 specifies EN 2491 for the MoS2 coating method. That matters because the coating affects driving behavior and the final coated condition of the screw.
• Designation - Clause 4 gives the ordering designation with a description block and an identity block, using the standard number, thread code and length code. The note also allows code I9005 to be inserted when needed, so buyers can place the correct reference on purchase documents.
• Marking - Clause 5 points to EN 2424 for marking and Table 3 links thread code groups to marking styles. This helps trace the part after manufacture and during receiving inspection.
• Technical specifications - Clause 6 points to EN 3818 and EN 3905. In practice, these are the companion documents that control the screw family and the six lobe recess technical details.

What terms does SIST EN 3725:2005 define?

• MJ thread - The aerospace thread form used for these screws, with limit dimensions taken from ISO 5855-2.
• Six lobe recess - The drive recess geometry used in the screw head, defined by EN 3911.
• MoS2 coating - A molybdenum disulphide dry lubricant coating applied under EN 2491.
• TI-P64001 - The titanium alloy named for the screw material.
• Strength class 1 100 MPa - The minimum tensile strength level stated for the screw material at ambient temperature.
• Normal shank - The shank form specified in the product title, meaning the screw has the defined shank geometry used by this family.
• Long thread - The thread extends to the head, as stated in the scope.

Who uses SIST EN 3725:2005?

SIST EN 3725:2005 is used by aerospace fastener manufacturers, design engineers, procurement teams, quality managers and inspectors. They use it to specify the screw on drawings and orders, check dimensions and marking, and confirm that the material, coating and recess form match the required aerospace part.

What changed in SIST EN 3725:2005 from the previous edition?

SIST EN 3725:2005 supersedes EN 3725:2003.

Which standards are used with SIST EN 3725:2005?

• ISO 3353-1 - Provides the aerospace lead and runout thread requirements for rolled external threads.
• ISO 5855-2 - Provides the MJ thread limit dimensions for bolts and nuts.
• EN 2424 - Sets the marking rules for aerospace products.
• EN 2491 - Specifies the coating methods for molybdenum disulphide dry lubricants.
• EN 3813 - Covers titanium alloy TI-P64001 in the condition used for forged fasteners.
• EN 3818 - Gives the technical specification for MJ-thread bolts in titanium alloy TI-P64001.
• EN 3905 - Gives the technical specification for six lobe recesses for bolts.
• EN 3911 - Defines the geometry of the six lobe recess.

What does the SIST EN 3725:2005 document contain?

The document contains a figure for the screw configuration and three tables that support ordering and inspection. Table 1 gives thread codes, dimensions and the related recess designation. Table 2 gives length codes, approximate masses and the combinations available across the thread sizes. Table 3 links thread code groups to marking styles.

Clause 4 shows how to build the designation using the standard number, thread code and length code, with an example format. Clause 5 points to the marking standard used on the product. Overall, the document is a dimensional and identification standard for one aerospace fastener family, used for design definition, procurement and conformity checks.