Surface finish Ra and Rz

Difference between the two parameters and when to specify each.

Ra is average; Rz is peak-to-valley. For bushing holes, Ra is enough; for seal seats, Rz is decisive.

Full article in production by the HannaTools R&D Team. This is the initial version published for indexing — updated continuously.

Topics covered

  • Definition and context
  • State of the art
  • Technical criteria
  • Application to Hanna HR®
  • Measurable metrics
  • Normative references