What is the difference between concentricity and coaxiality?

What is the difference between concentricity and coaxiality?

• A. Concentricity governs two axes to be coaxial; coaxiality relates a feature’s center axis to a datum axis.
• B. Concentricity relates a feature’s center axis to a datum axis; coaxiality governs two axes to be coaxial.
• C. Concentricity measures runout; coaxiality measures parallelism.
• D. Concentricity is about surface texture; coaxiality is about symmetry.

Answer: (B)

The key idea is how axes line up. Concentricity is about the center axis of a cylindrical feature in relation to a reference datum axis. It uses the centerline of the feature and requires that center axis lie within a cylindrical tolerance zone coaxial with the datum axis, effectively matching the feature’s centerline to the datum axis. Coaxiality, on the other hand, is about the axes themselves. It requires two axes (the feature’s axis and a datum axis, or two feature axes) to be coaxial with each other within the specified tolerance. So the best choice captures that distinction: concentricity relates a feature’s center axis to a datum axis, while coaxiality governs two axes being coaxial. The other statements mix in runout, surface texture, parallelism, or symmetry, which aren’t the definitions here.

The key idea is how axes line up. Concentricity is about the center axis of a cylindrical feature in relation to a reference datum axis. It uses the centerline of the feature and requires that center axis lie within a cylindrical tolerance zone coaxial with the datum axis, effectively matching the feature’s centerline to the datum axis.

Coaxiality, on the other hand, is about the axes themselves. It requires two axes (the feature’s axis and a datum axis, or two feature axes) to be coaxial with each other within the specified tolerance.

So the best choice captures that distinction: concentricity relates a feature’s center axis to a datum axis, while coaxiality governs two axes being coaxial. The other statements mix in runout, surface texture, parallelism, or symmetry, which aren’t the definitions here.