These embroidery hoops are made of plastic. Plastic embroidery hoops often have a groove or lip on the inside where the inner hoop locks into the outer hoop, in addition to having the screw hardware to tighten the hoops together. This makes for a snug fit and allows the fabric to be held taut for hand embroidery projects. It's size is 25cm. Random Color depending on available stocks :) Available Sizes: Size 4 - 10cm Size 6 - 16cm Size 7 - 18cm Size 8 - 20cm Size 10 - 25cm