Question

As per the Indian standards, the limits and fits specify how many grades of tolerances?

• A. 10
• B. 18
• C. 22
• D. 28

Hint:

Remember the standard classification system values: - Number of standard tolerance grades = 18 - Number of fundamental deviations = 25 (extended to 28 in newer standards, but fundamental categories remain distinct).

Answer 1

The Correct Option is B

Concept: The Indian Standard (IS:919) system of limits, fits, and tolerances aligns closely with the international ISO system to govern component variability during manufacturing.
• Standard Tolerances (IT Grades): Define the magnitude of the manufacturing zone tolerance. There are 18 fundamental tolerance grades denoted as: \[ \text{IT01, IT0, IT1, IT2, IT3, \dots, IT16} \]
• Fundamental Deviations: Define the location of the tolerance zone relative to the zero/basic line. There are 25 fundamental deviations for shafts and holes (denoted by letters like A–ZC and a–zc).

Step 1: Quantify the total number of IT grades. Counting the sequential categories from IT01 up to IT16: - IT01 and IT0 (2 grades) - IT1 through IT16 (16 grades) Total = $2 + 16 = 18$ standard grades. Lower numbers (e.g., IT01 to IT5) represent tight tolerances for high-precision tools like gauges, while higher numbers (e.g., IT12 to IT16) correspond to looser tolerances for operations like sand casting or rough forging.