20 to 50 caliber is 8-32 threaded brass coupler. Easy to Use: it easy to maneuver the brush through the barrel, and the brushes are designed to fit snugly in the cleaning rod for secure use. The McJ Tools Rifle Bronze Bore Brush Set includes 20 brushes that are perfect for cleaning the 270 Cal gun barrel to ensure it is free of debris, fouling, and other contaminants.