What follows is a short summary of feature control symbols used in GDT. As was mentioned in the introduction, this is not intended to be an exhaustive presentation of GDT, but rather a concise, clear explanation of GDT's most important yet often misunderstood points. Therefore, we do not explain in detail all of the symbols listed below. |
In the "Type of Feature" column, "Individual" means that this type of tolerance does not need to be referred to a datum. Individual GDT tolerances are the easiest to understand for a beginning GDT user. "Related" designates a type of tolerance that must be referred to a datum. "Individual or Related" can be of either type, depending on the situation.
|TYPE of TOLERANCE||TYPE of FEATURE||NOTES|
|Concentricity||Location||Related||Difficult to inspect.|
|Total Runout||Runout||Related||Includes Circular Runout|
|Profile of a Surface||Profile||Individual or Related|
|Profile of a Line||Profile||Individual or Related|
|Roundness or Circularity||Form||Individual|