Felton's, made in Canada T5 twisted tube brushes are available with steel, stainless, or brass wire fill. Perfect for cleaning out small tubes, drill holes or any small, confined spaces. High grade USA brass wire, ideal in non-sparking and softer, sensitive material fabrication. NOTE: The inside diameter of the flue is approximately 1/4" smaller than the outside diameter. The diameter of the flue brush will equal the inside diameter of the flue.