Which of the following grades is NOT part of the ISO Comparator grading system?

The ISO Comparator grading system is used to classify the roughness of surfaces based on the particle size of solid materials. Each grade within this system is defined by specific particle size ranges that correlate with surface texture and finish.

The ultra-fine grade does not exist within this classification system. Instead, the grades that are part of the ISO Comparator system include finer-than-fine grade, medium grade, and coarse grade, which categorize surfaces based on increasingly larger particle sizes. These existing grades allow inspectors to effectively evaluate surface conditions for coating applications.

The absence of an ultra-fine grade in the ISO grading system is significant because it highlights the specific focus of the system on defining surfaces that are more relevant to practical applications in coatings and surface preparation. Understanding which grades are officially recognized is crucial for inspectors when assessing and recommending appropriate coating procedures and materials.