ISO 5856:2008

Overview

ISO 5856:2008 defines the dimensions for a specific family of aerospace screws: 100° normal countersunk head screws with an internal offset cruciform drive (ribbed or unribbed), normal shank, and short or medium MJ threads. Applicable to metallic screws (coated or uncoated) with strength classes ≤ 1 100 MPa, this International Standard supports the compilation of aerospace product standards and replaces the 1991 edition.

Key topics and technical requirements

• Head and drive: 100° normal countersunk head with internal offset cruciform drive; options include ribbed or unribbed drives.
• Thread form: Short or medium length MJ threads (metric aerospace thread form) specified for bolts and screws.
• Shank tolerances: Covers close or large tolerance normal shank dimensions; specifies max/min diameters and tolerances.
• Material and finish: Applies to metallic materials, whether coated or uncoated; dimensions and tolerances are given after coating (with some pre-coating shank tolerances specified for heat-cured matrix coatings).
• Strength classes: Intended for fasteners with tensile strength classes up to 1 100 MPa.
• Units and tolerancing: All dimensions and tolerances in millimetres. Tolerances of form and position default to ISO 7913 unless otherwise stated.
• Applicability: Intended for use in aerospace product standards; details of form not stated are left to the manufacturer’s discretion.
• Reference standards: Normative cross-references include ISO 286-2 (limits & fits), ISO 3353-1 (rolled external threads), ISO 5855-2 (MJ threads limits), ISO 7913 (form/position tolerances), and ISO 14275/14276 (internal offset cruciform drives).

Applications and users

ISO 5856:2008 is practical for:

• Aerospace designers and engineers specifying countersunk fasteners for structural and interior applications.
• Fastener manufacturers producing aerospace screws to defined dimensional criteria.
• Quality, inspection, and metrology teams verifying screw dimensions, tolerances, and coating allowances.
• Procurement and supply chain professionals ensuring purchased fasteners conform to aerospace product standards.
• Standards committees compiling component-level aerospace specifications.

Typical applications include flush-mounted countersunk fastenings in airframes, interiors, assemblies where low-profile heads and controlled thread/shank geometry are critical.

Related standards

• ISO 5855-2 - MJ threads - limit dimensions for bolts and nuts
• ISO 7913 - Aerospace bolts and screws: tolerances of form and position
• ISO 14275 / ISO 14276 - Internal offset cruciform drives (ribbed and unribbed)
• ISO 286-2 - Limits and fits tables
• ISO 3353-1 - Rolled external threads

Keywords: ISO 5856:2008, aerospace screws, 100° countersunk head, internal offset cruciform drive, MJ threads, aerospace fasteners, dimensions, tolerances, strength classes.