Millwright Level 1 Practice Exam

In a general purpose ISO metric thread designation, which character indicates a medium tolerance grade?

1. Grade 7

2. Grade 5

3. Grade 6

4. Grade 8

The correct answer is: Grade 6

In ISO metric thread designation, the tolerance grade is crucial for determining the fit between mating threads. The medium tolerance grade is specifically indicated by Grade 6. This grade is widely accepted as the standard for general applications, providing a balance between ease of assembly and strength of the threaded connection. Grades lower than 6 (like Grade 5) offer tighter tolerances and are typically used for precision applications, while grades higher than 6 (like Grade 7 or Grade 8) indicate looser tolerances, which might not provide the best fit for general-purpose use. Understanding these designations helps in selecting the appropriate thread for a specific application, ensuring compatibility and performance in mechanical assemblies.