Seal groove surface finish requirements per API 6A are 32 µin Ra maximum for elastomeric O-ring grooves and 16 µin Ra for metal seal contact areas. Poor surface finish leads to extrusion damage and leakage. Manufacturers use single-point diamond turning or honing with expandable mandrels to achieve consistent finish and geometry in high-alloy materials that are difficult to machine https://globalsealstech.com/product-category/oil-gas-seals/api-6a-gate-valve-seals/