What are the three ways to size twist drills?

The correct method for sizing twist drills is best represented by inches, letter, and number. This sizing system allows users to categorize twist drills based on specific measurements and standards commonly utilized across different applications.

Inches refer to the actual diameter of the drill bit measured in fractional sizes, which is a traditional method used especially in the United States. The letter sizing system provides a range of drill sizes that are not defined by standard either fractional or metric measurements, useful for identifying drill bits within a certain size range without resorting to exact measurements. The number size system, typically used for smaller drill bits, helps to designate sizes that can be more finely categorized than fractional inch measurements.

Understanding this sizing system is crucial for selecting the appropriate drill bit for a given task, ensuring that the drill can effectively penetrate the material while achieving the desired hole size. Knowing how to interpret these categories enables precise and effective drilling operations necessary in aviation structural maintenance and repair.