.35-.40 Cal. Mop Fits: .357/.380 Cal./.38 Cal./9mm/.40 Cal/10mm These bore mops are 100% cotton with 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. American Standard #8/32 thread.