Rico Design Embroidery Hoop is made of plastic and available in a range of diameters. With its particularly firm hold, this embroidery hoop guarantees unlimited embroidery fun! The inner ring of the hoop has a groove, which "clicks" into the groove of the outer ring. This gives the canvas a firm hold and prevents it from slipping during your work. Clamping is very easy when the metal screw is completely loosened: simply place the outer ring around the inner ring and then fasten the screw again.