This kit contains 11 spools (1094 yds each) of 40 weight Aurifil thread to buttonhole stitch around the appliqué shapes in the "My Magical Garden" Quilt-Along and one spool of 50 weight Aurifil beige piecing thread. The colors are hand selected to match the appliqué fabric kits. Using 40 weight thread gives a beautiful finish to your buttonhole stitch appliqué. The thicker thread builds up against the edge of the appliqué shapes, doing a great job of camouflaging the cut edges of fused appliqué. The thicker thread also helps prevent fraying along the raw edges of the appliqué. Some threads work for more than one fabric in the fabric kit, that is why there are 11 colors and a neutral for piecing even though there are 18 appliqué fabrics in the BOM quilt.