What is coaxiality in GD&T?

• A. The tolerance that two or more features share a common axis
• B. Tolerance for concentricity
• C. Tolerance for perpendicularity
• D. The requirement that two holes be the same size

Answer: (A)

Coaxiality is about making sure the axes of cylindrical features share a common axis within a specified tolerance. In practice, you designate a reference datum axis and require the axis of another feature to lie inside a cylindrical tolerance zone that is coaxial with that datum axis. This ensures those features run or assemble along the same line, which is crucial when a shaft or through-hole must align perfectly through multiple features.

So the best fit is that coaxiality controls the tolerance for two or more features to share a common axis. It’s not about concentricity, which deals with the centerlines in a different sense, not about perpendicular relationships, and it isn’t simply about two holes being the same size.