The brush knots are knotted to 75% of the length. Aggressive brush. Excellent for cleaning the external diameter of pipes. Steel wire is the most common filament material. Brushes with steel wire as the filament material are ideal for work on surfaces and deburring. PFERD special wire has high tensile strength and bending fatigue strength. This ensures that the wire wears down in the optimal way, as well as a long tool life, even in extreme brushing applications. Steel wire is temperature-resistant up to 600°F.