A wool bore mop sized for .338 barrels. It is used after brushing to soak up loosened fouling and leftover solvent, and with a few drops of gun oil it lays down a thin protective film that helps prevent rust in storage. Screw it onto a cleaning rod with a matching thread and push it through the bore several times until it comes out clean. Wool is soft and will not mark the rifling or the inside of the barrel. Replace the mop once it becomes dirty or matted, and check that the thread suits your rod before use.