A TNUT is a type of fastener that leaves a flush surface. It is a type of nut that has a flat bottom and a cylindrical top, which allows it to sit flush with the surface of the material it is being attached to. It is commonly used in applications where a smooth, flush surface is desired, such as in furniture or cabinetry. The TNUT is a versatile fastener that can be used in a variety of materials, including wood, metal, and plastic.