ANS:A - alphabetical letter.

"alphabetical letter" specifically denotes a letter from the alphabet that corresponds to a specific range of hardness. In the context of grinding wheels, different letters are used to categorize wheels based on their hardness. This classification system helps users select the most suitable grinding wheel for their specific application, taking into account factors such as the material being ground, the desired surface finish, and the aggressiveness of the grinding operation. Here's a brief overview of the commonly used alphabetical classification system for grinding wheels:

• Soft Grades: Grinding wheels designated with letters from A to H are considered soft grades. These wheels are relatively softer and more friable, meaning they are able to break down more easily under pressure. They are suitable for grinding materials that require cooler cutting and less heat generation, such as high-speed steel, stainless steel, and non-ferrous metals.
• Medium Grades: Grinding wheels designated with letters from I to P fall into the medium-grade category. These wheels strike a balance between hardness and friability, making them versatile for a wide range of grinding applications. They are commonly used for grinding materials like carbon steel, alloy steel, and cast iron.
• Hard Grades: Grinding wheels designated with letters from Q to Z are considered hard grades. These wheels are relatively harder and less friable, meaning they retain their shape and cutting ability under high-pressure grinding conditions. They are suitable for grinding hard materials that require aggressive stock removal and longer wheel life, such as tool steels, hardened steels, and ceramics.

Each letter in the alphabetical classification system represents a specific range of hardness, with A being the softest and Z being the hardest. By selecting the appropriate letter designation, users can ensure they have the right grinding wheel for their application, optimizing performance, efficiency, and surface finish.