A piece of fabric used to cover a crack in a nail is known as a:

A repair patch is specifically designed to effectively cover and reinforce a crack in a nail. Its primary function is to provide support and protection to the affected area, ensuring that the crack does not worsen and that the integrity of the nail is maintained. The materials used in a repair patch are typically durable yet flexible, allowing for a seamless finish that blends with the natural nail.

In contrast, other terms might describe different products or techniques related to nail care but do not directly refer to the process of covering a crack. For instance, a support strip may refer to a broader category of reinforcement used in various contexts but isn't specifically formulated for nail repair. A nail swathe does not have a recognized meaning in standard nail care, and a stress strip may refer to reinforcement in nail enhancements but doesn't specifically align with the idea of patching a crack as effectively as a repair patch does. Thus, the use of a repair patch is the most accurate term for this technique.