This Brush Is Designed For The Chimney Sweep’s Special Needs. Its construction is identical to the Master Sweep brush, but instead of round wire, flat oil-tempered wire is used. Some sweeps prefer flat wire brushes because of the greater contact area afforded by each filament. These brushes are also shorter than standard wire brushes, thus giving greater flexibility in going around offsets and through elbows. This brush is now using much stiffer wire than the original Flat Wire brush introduced in 198112'' x 12'' Square Flat Wire Brush - 3/8'' thread