An embroidery hoop consists of a pair of concentric circular rings. The larger ring has a tightening device, usually in the form of a metal screw, to keep the fabric held between taught. The artisan repositions the hoop as needed when working over a large piece of fabric. Embroidery hoops come in various sizes and are generally small enough to control with one hand and rest in the lap.  modern hoops are made of wood or plastic.