prEN 3381

prEN 3381 is a CEN draft European Standard for aerospace screws with a 100° countersunk normal head, offset cruciform recess, close tolerance normal shank, short thread, in titanium alloy, anodized and MoS2 lubricated. It specifies the characteristics and identification rules for screws in strength class 1 100 MPa at ambient temperature and 315 °C maximum temperature, so manufacturers, inspectors and buyers can describe the same fastener form, material, finish and marking.

What does prEN 3381 specify?

prEN 3381 specifies the characteristics of one aerospace screw family and the rules used to identify, mark and qualify it. The standard is arranged in clauses 1 to 8, covering scope, normative references, terms and definitions, required characteristics, designation, marking, technical specification and oversized bolts.

Clause 4 gives the product requirements for configuration, dimensions, tolerances, materials and surface treatment. Clauses 5 and 6 cover how the screw is designated and how it is marked. Clause 7 sets the technical specification basis for supply and qualification, and Clause 8 links oversized bolts to EN 4016.

What are the key requirements of prEN 3381?

prEN 3381 ties the screw definition to a fixed geometry, controlled materials and a specific surface condition. In practice, that means the drawing, material certificate, finish and identification code all have to match the same standard family.

• Clause 4.1 requires the configuration to follow Figure 1 and the dimensions and mass to follow Table 1. The dimensions are given in millimetres and are checked after anodizing but before lubricating, which matters when measuring finished parts.
• Clause 4.2 sets form and position tolerances by reference to ISO 7913, so inspection is based on a separate aerospace tolerance standard rather than on local drawing practice.
• Clause 4.3 allows the screw material to come from TR 3775 or SAE AMS4967, both for titanium in strength class 1 100 MPa. This gives purchasers a controlled material route instead of an open material choice.
• Clause 4.4 requires a MoS2 lubricant from TR 4070 and application in accordance with EN 2491. The finish and lubricant are part of the part definition, so surface treatment is not just a cosmetic step.
• Table 1 fixes the MJ thread family, diameter and length coding, and the special thread requirement that the major diameter follows the stated relationship to the minimum diameter. This is the main size-control part of the standard.
• Clause 5 defines designation by code elements for hole, diameter, length, drive and lubricant. That matters for ordering, stock control and traceability because the code carries the part definition.
• Clause 6 defines marking in the EN 2424 style and links the marking code to the diameter range. That helps inspection and receiving checks identify the part without ambiguity.
• Clause 7 requires aerospace production control, an accepted quality management system and documented qualification of the screws. In practice, suppliers need both process control and proof that the product has been qualified to the specified tests.

What terms does prEN 3381 define?

prEN 3381 uses a small set of technical terms and abbreviations in its requirements.

• MJ thread - The aerospace metric thread form used for these screws.
• Offset cruciform recess - The internal drive recess used for the screwdriver or bit engagement.
• MoS2 - Molybdenum disulphide, used here as the dry lubricant on the screw.
• QMS - Quality management system, the controlled production system expected from the manufacturer.
• EN 2424 style - The aerospace marking style used for product identification.
• Classification 1 100 MPa/315 °C - The strength and temperature class assigned to the screw family, linking mechanical capability and service temperature.

Who uses prEN 3381?

prEN 3381 is used by aerospace fastener manufacturers, procurement teams, quality managers and inspection personnel. It also supports test and qualification organizations that verify material, finish, dimensions, marking and production control.

For buyers, it gives a precise ordering basis. For engineers, it gives the geometry, thread and surface-treatment constraints needed for design and interchangeability. For quality teams, it gives the references used to check conformance and supplier qualification.

What changed in prEN 3381 from the previous edition?

prEN 3381:2026 supersedes EN 3381:2025. The stated changes are updated normative references, an updated Figure 1 and editorial updates.

Which standards are used with prEN 3381?

• EN 2424 - Gives the marking practice for aerospace products.
• EN 2491 - Gives coating methods for MoS2 dry lubricants.
• EN 4016 - Covers oversized bolts, which Clause 8 uses for oversized variants.
• ISO 3353-1 - Covers lead and runout threads for rolled external threads.
• ISO 5855-2 - Gives MJ thread limit dimensions for bolts and nuts.
• ISO 5856 - Gives dimensions for 100° countersunk-head aerospace screws with MJ threads.
• ISO 7913 - Gives tolerances of form and position for aerospace bolts and screws.
• ISO 9152 - Gives the procurement specification base for titanium bolts with MJ threads.
• ISO 14275 / ISO 14276 - Define the offset cruciform drive options used in the designation.
• TR 3775 - Lists titanium bolt and pin materials used by this standard.
• TR 4070 - Lists commercial MoS2 coating products.
• EN 9100 / EN 9133 - Support the quality management and qualification approach named in Clause 7.

What does the prEN 3381 document contain?

prEN 3381 contains a configuration figure, a dimensions-and-mass table, and tables for hole codes, drive codes and marking. It also contains the technical specification clause that ties the product to aerospace production control and qualification.

For engineering and inspection work, the document is mainly a reference for shape, size, thread form, material, surface treatment and coding. For procurement and quality records, it is the basis for the designation string, product marking and supplier qualification evidence.