Plastic sided prewound bobbin threads feature clear plastic sides that will not distort or absorb machine oils, with a clear case for easy collection and classification. Size A Class 15 (SA156) prewound bobbin threads are compatible with various embroidery and sewing machines. Black color threads meet basic requirements for Diy embroidery and sewing projects. Made from high tenacity polyester filament 70D/2 (60WT), these threads provide consistent draw-off tension from beginning to end by reducing friction and static charge during embroidery and sewing operations.