Pro Shot Products 10-12-16 Ga. Mop. Shotgun Bore mop made with 100% cotton and a brass core. They are made of the highest quality construction possible. Mops can be used for quick cleaning and bore lubrication. Mops are especially excellent when using oil for bore lubrication because they create foaming action that helps in the lubrication process. Standard American Shotgun #5/16-27 thread.