imported nylon,wear-resistant,flexible,suitable for condenser tubes cleaning, diameter can be 1/4~1", metric M6 brush thread Specifications:Available for tube sizes 1/4"-1" Cleaning Diameter(inch)(mm)0.256.40.317.90.389.50.4411.10.5012.70.5614.30.6315.90.6917.50.8819.10.8120.60.8822.20.9423.81.0025.4 Condenser Brush (round cleaning brush,copper tube brush,chiller brush)