"Conveniently packaged the 13-piece caliber-specific set of Best Bore Brushes means that you always have the right brush at hand. Contained in a durable hinged box with marked cavities its easy to select the correct Bore Brush for your particular application. Because they are caliber specific you can be assured of an optimum fit to your firearms bore for efficient and thorough cleaning. .17-.45 calibers. All brushes have 8-32 threads (17 and 20 caliber have 5-40 threads and is a standard bore brush.