F4 Wiki

The public, stable reference for GD&T and how the F4 Application interprets it. Each topic pairs standard GD&T guidance with F4 validation behavior so you can move from definition to decision quickly.

Quick links

Start here

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Standard definitions, symbols, and usage guidance.

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Rules, checks, and decisions used by the F4 validator.

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Short definitions and worked applications.

Browse by category

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Straightness, flatness, circularity, cylindricity.

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Parallelism, perpendicularity, angularity.

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Position, composite, MSS, concentricity, symmetry.

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Line, surface, composite, MSS.

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Circular and total runout.

Supporting rules

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Featured pages

GDT:Straightness - basic line element form control.
GDT:Flatness - planar form control.
GDT:Position - primary location control for features of size.
GDT:Profile of a Surface - shape and location combined.
F4:Position Validation - how F4 checks position.

How to use this wiki

The public view shows approved revisions only.
Each GD&T page links to its matching F4 validation page.
Use the sidebar or search to find topics quickly.
When a rule needs interpretation, the F4 page calls out the decision and its impact.

Community

Community forum

Announcements, questions, feature requests, and showcases.

Messages

Direct messages between contributors.

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