imported nylon,wear-resistant,flexible,suitable for condenser tubes cleaning, diameter can be 1/4~1", metric M6 brush thread ... -EXCHANGER TUBES CLEANINGSpecifications:Available for tube sizes 1/4"-1" Cleaning Diameter(inch)(mm)0.256.40.317.90.389.50 ... .60.8822.20.9423.81.0025.4 Nylon Tube Brush (round cleaning brush,copper tube brush,chiller brush)