Answer
Feb 07, 2026 - 01:18 PM
A 0.4 surface finish refers to a surface roughness value of 0.4 micrometers (µm) Ra, where "Ra" stands for "roughness average." This indicates a very smooth and finely machined surface, commonly achieved through precision grinding, lapping, or polishing processes. Such a finish is often required for high-precision engineering components to reduce friction and wear.
