ISO 13921:2008

Aerospace - Screws, 100 degrees reduced countersunk head, internal offset cruciform ribbed or unribbed drive, normal shank, short or medium length MJ threads, metallic material, coated or uncoated, strength classes less than or equal to 1 100 MPa - Dimensions

ISO 13921:2008 specifies the dimensions of 100° reduced countersunk head screws with internal offset cruciform ribbed or unribbed drive, with close or large tolerance normal shank and short or medium length MJ threads, in metallic material, coated or uncoated, with strength classes less than or equal to 1 100 MPa. ISO 13921:2008 is applicable to the compilation of aerospace product standards.

Aéronautique et espace — Vis à tête fraisée 100 degrés réduite, à empreinte cruciforme déportée, avec ou sans saillies antidérapantes, à tige normale et filetages MJ courts ou de longueur moyenne, en matériau métallique, revêtues ou non revêtues, des classes de résistance inférieures ou égales à 1 100 MPa — Dimensions

General Information

• Status: Published
• Publication Date: 17-Aug-2008
• ICS: 49.030.20 - Bolts, screws, studs
• Technical Committee: ISO/TC 20/SC 4 - Aerospace fastener systems
• Drafting Committee: ISO/TC 20/SC 4 - Aerospace fastener systems
• Current Stage: 9093 - International Standard confirmed
• Start Date: 21-Nov-2025
• Completion Date: 13-Dec-2025

Relations

• Revises: ISO 13921:1996 - Aerospace - Screws, 100 degrees reduced countersunk head, internal offset cruciform ribbed or unribbed drive, normal shank, short or medium length MJ threads, metallic material, coated or uncoated, strength classes less than or equal to 1 100 MPa - Dimensions
• Effective Date: 15-Apr-2008

Overview

ISO 13921:2008 is an international aerospace standard that specifies the dimensions for 100° reduced countersunk head screws with an internal offset cruciform (ribbed or unribbed) drive. Published as the second edition in 2008, ISO 13921:2008 replaces the 1996 edition and is intended for use in the compilation of aerospace product standards. The standard covers screws with normal shank (close or large tolerance), short or medium length MJ threads, metallic material (coated or uncoated), and strength classes ≤ 1 100 MPa. Dimensions and tolerances are expressed in millimetres.

Key topics and technical requirements

• Head and drive geometry: 100° reduced countersunk head with internal offset cruciform drive - available ribbed or unribbed for anti-slip features.
• Threads and shank: MJ series threads (short or medium length) and normal shank with close or large tolerance options.
• Materials and finishes: Metallic screws, coated or uncoated; dimensions apply after coating but before lubrication (with specific pre-coating shank tolerances noted for some coatings).
• Strength classes: Applicable to screws with strength classes less than or equal to 1 100 MPa.
• Dimensions and tolerances: Provided in millimetres via figure(s) and Table 1 in the standard; tolerances of form and position default to ISO 7913 unless otherwise stated.
• Normative references: Interacts with other standards such as ISO 286-2 (limits and fits), ISO 3353-1 (lead/runout threads), ISO 5855-2 (MJ threads limits), ISO 7913 (form/position tolerances), ISO 14275 and ISO 14276 (internal offset cruciform drives).

Applications and users

ISO 13921:2008 is used wherever consistent, interchangeable aerospace fasteners are required:

• Aerospace OEMs and tier suppliers specifying screw dimensions on component drawings and product standards.
• Fastener manufacturers producing MJ-threaded, reduced countersunk screws for aircraft and spacecraft hardware.
• Design and mechanical engineers selecting screws for flush mounting, structural and secondary assemblies.
• Procurement and quality assurance teams verifying dimensional conformity and acceptance criteria.
• Maintenance and repair organizations ensuring replacement parts meet original specification for safety and airworthiness.

Related standards

• ISO 286-2 - Limits and fits (tolerance grades)
• ISO 3353-1 - Lead and runout threads (rolled external threads)
• ISO 5855-2 - MJ threads - limit dimensions for bolts and nuts
• ISO 7913 - Tolerances of form and position for bolts and screws
• ISO 14275 / ISO 14276 - Internal offset cruciform drives (ribbed/unribbed)

Keywords: ISO 13921:2008, aerospace screws, 100° reduced countersunk head, internal offset cruciform drive, MJ threads, screw dimensions, aerospace fastener standards.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 13921
Second edition
2008-08-15
Aerospace — Screws, 100 degrees
reduced countersunk head, internal offset
cruciform ribbed or unribbed drive,
normal shank, short or medium length MJ
threads, metallic material, coated or
uncoated, strength classes less than or
equal to 1 100 MPa — Dimensions
Aéronautique et espace — Vis à tête fraisée 100 degrés réduite,
à empreinte cruciforme déportée, avec ou sans saillies antidérapantes,
à tige normale et filetages MJ courts ou de longueur moyenne, en
matériau métallique, revêtues ou non revêtues, des classes de
résistance inférieures ou égales à 1 100 MPa — Dimensions

Reference number
©
ISO 2008
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Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 13921 was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 4, Aerospace fastener systems.
This second edition cancels and replaces the first edition (ISO 13921:1996), which has been technically
revised.
INTERNATIONAL STANDARD ISO 13921:2008(E)

Aerospace — Screws, 100 degrees reduced countersunk head,
internal offset cruciform ribbed or unribbed drive, normal shank,
short or medium length MJ threads, metallic material, coated or
uncoated, strength classes less than or equal to 1 100 MPa —
Dimensions
1 Scope
This International Standard specifies the dimensions of 100° reduced countersunk head screws with internal
offset cruciform ribbed or unribbed drive,
...