KEYSTONE Flame Retardant Sewing Thread Supply High Mechanical Strength, Flame Retardance, Abrasion Resistance and Smooth Surface KEYSTONE Flame Retardant Sewing Thread Supply High Mechanical Strength, Flame Retardance, Abrasion Resistance and Smooth ... . Application: Glove, Bag, Mattress, Shoe, Uniform, Filter bag, etc4. Package: Sewing Thread Cone+Poly Cover