Perfect for anyone who applies flat backs to clothing, costumes, paper arts and home decor items. There are over 1000 pieces in the eight most popular sizes for acrylic flat back projects in each box. The round sizes are 4mm, 6mm, 8mm, 10mm, and 12mm and in the oval 8x10mm, 10x14mm, and 13x18mm. For easy storage and convenience they come in a plastic box with a lid.