A path through GD&T, from datums to runout.

The path

1. Stage 1

   Start here

   What GD&T is for, how to read a drawing that uses it, and the three things every callout is built from.

   1. 01The GD&T Guide: Everything you need to create professional drawingsWhy GD&T exists, design intent, and the four things a tolerance can control: size, location, orientation and form.
   2. 02How to Read a GD&T Drawing: Insights from R. Dean OdellReading a GD&T drawing in order: the title block, the general notes, then the views and the callouts.
   3. 03DatumsWhat a datum is, the six degrees of freedom, and how datums constrain them.
   4. 04Feature Control FramesThe compartments of a feature control frame, what each one holds, and the part the datum references play.
   5. 05Basic DimensionsWhat a basic dimension is, why it carries no tolerance of its own, and where the tolerance comes from instead.

2. Stage 2

   Form

   Shape on its own terms, with no datum: is the surface or the axis the shape the drawing says?

   1. 06FlatnessFlatness of a surface: what it controls, how it goes on a drawing and how it is measured.
   2. 07StraightnessStraightness of a surface line or an axis, and what a material condition modifier changes.

3. Stage 3

   Orientation

   A feature's angle to a datum: parallel, perpendicular, or at a stated angle.

   1. 08ParallelismParallelism to a datum: how it looks on a drawing and how it is inspected.
   2. 09PerpendicularityPerpendicularity to a datum: how it is applied on a drawing and how it is measured.
   3. 10AngularityAngularity at a stated angle to a datum: on the drawing and at inspection.

4. Stage 4

   Location and profile

   Where a feature sits relative to its datums, and the control that can hold a surface's shape and location at once.

   1. 11PositionPosition: the tolerance zone around true position, how it is called out and how to read one.
   2. 12ProfileProfile: what it controls on a surface, how it goes on a drawing and how it is measured.

5. Stage 5

   Runout

   Parts that turn: how far a surface moves as the part rotates about a datum axis.

   1. 13RunoutCircular and total runout: how each is applied and how each is inspected.

6. Stage 6

   Putting it to work

   Where the tolerances meet a real part: fits, stack-ups and designing for the shop.

   1. 14Why Your Dowel Pin Doesn’t Fit, and How to Fix ItTolerance zones, hole-basis and shaft-basis fits, clearance and allowance, and what H7/g6 means.
   2. 15Why your tolerance stack-up keeps failing & FREE spreadsheet to fix itAdding tolerances along a chain of parts to check a gap or a fit, with a free spreadsheet.
   3. 16Master the Basics of DFM (& finally show your machinist some love)Designing for CNC machining, injection molding and sheet metal, so the shop can make the part.

Every article, newest first, is on the blog .

The symbols

The geometric tolerances, grouped by type.

As the GD&T Cheat Sheet groups them, with what each one controls. Each zone is drawn far wider than scale. The cheat sheet turns every zone in 3D, with a drawing and an inspection setup for every row.

Profile of a line uses the same arc without its base and controls one cross section at a time. The chart and the profile guide cover profile of a surface; the cheat sheet's profile card shows both zones.

Free tools

The same work, on your own drawing.