Which type of screws displace material to form threads without removing swarf?

Thread-forming screws are designed to create threads in a workpiece by displacing material rather than cutting it away. This process is often referred to as "cold forming," where the material of the workpiece is displaced to accommodate the threads of the screw. This method allows the screw to maintain material integrity and strength, resulting in tight fits and enhanced resistance to stripping.

The key advantage of thread-forming screws is that they eliminate the need for cutting chips or swarf, which is advantageous in applications where cleanliness is a priority or in automated assembly processes where the removal of debris can be problematic. By forming threads rather than cutting them, these screws can also create tighter threads with a more reliable hold in various materials, including plastics and softer metals.

In contrast, other types of screws, such as thread-cutting or self-tapping screws, do involve some removal of material to create the threads, resulting in swarf or debris. Hexagon screws refer to the shape of the head and are not specifically related to how the threads are formed. Thus, the unique characteristic of thread-forming screws makes them the appropriate answer to the question.