Small geometric variations can add at the entry
- Flatness
The surface must remain within its specified flatness zone. Assess the sealing land over the relevant contact area.
- Concentricity / eccentricity
Two centres are displaced in the example. Check the specified relationship; concentricity and eccentricity are not interchangeable measurements.
- Surface roughness (Ra)This term
The profile varies around a reference line. Ra is a defined average measure, not a complete description of every sealing-surface defect.
- Tolerance stack
Variation from several dimensions combines in the assembled gap or reach. Review the resulting limits rather than nominal dimensions alone.
Flatness, alignment, texture and accumulated dimensions describe different aspects of fit. A nominally correct hole can still have an unsuitable sealing face or alignment.
Exaggerated geometry and qualitative profiles. Symbols and limits on the actual drawing govern the inspection; this figure is not a tolerance specification.