Description Madeira Aerofil No. 35 is an extra strong, soft furnishing thread with the perfect weight and texture for buttonholes or top stitching on heavy fabrics, such as denim, leather, suede and more. It features the same strength and smooth running qualities of our regular Aerofil thread. Madeira’s more traditional spool shape eliminates the “drop off” and tangling problems associated with the elongated spools many other manufacturers use. And, all Madeira spools come with double locking end caps to keep thread neat and tidy.