Foundation 01
Datums
The reference system that makes a drawing repeatable in inspection and assembly.
Read the guide →GD&T foundations
Build the language
behind the drawing.
Learn the concepts that make feature control frames, tolerance zones, and inspection setups understandable.
Foundation guides
The ideas behind every
GD&T callout.
Start with datums and feature control frames, then work through material conditions, basic dimensions, and the inspection concepts that connect a drawing to a real part.
Foundation 02
Feature Control Frames
The boxed instruction that tells you what is controlled, how much variation is allowed, and what it is referenced to.
Read the guide →Foundation 03
Maximum Material Condition (MMC)
A material-condition modifier that protects functional fit while allowing useful manufacturing freedom.
Read the guide →Foundation 04
Least Material Condition (LMC)
A material-condition modifier used when the least amount of material is the functionally critical condition.
Read the guide →Foundation 05
Basic Dimensions & Tolerance Zones
The exact targets and allowable spaces that turn drawing intent into an inspectable requirement.
Read the guide →Foundation 06
Regardless of Feature Size (RFS)
The default relationship when a geometric tolerance is not modified by MMC or LMC.
Read the guide →Foundation 07
Rule #1 & Features of Size
How size limits and form relate for regular features such as holes, shafts, and opposed parallel surfaces.
Read the guide →Foundation 08
Virtual Condition & Functional Gaging
A worst-case assembly boundary and the practical gages often used to verify it.
Read the guide →Foundation 09
Datum Feature Modifiers & Datum Shift
How material-boundary modifiers on datum references can allow functional movement in a datum setup.
Read the guide →Foundation 10
Composite Position
A two-segment position control for patterns that must locate to datums and stay tightly related to one another.
Read the guide →