How are torx sizes determined?

Torx sizes are determined by the diameter of the drive socket and the number of points (or lobes) in the star-shaped design. The sizes are typically specified by a letter and a number, where the letter indicates the series and the number corresponds to the specific size within that series. For example, a T10 size has a specific diameter and point count that distinguishes it from other sizes like T15 or T20. This standardized sizing allows for compatibility across various tools and fasteners.