These brushes feature stiff nylon bristles wrapped in an aluminum core and male-threaded coupling. The absence of brass in their construction eliminates the false positive indications of copper fouling that can occur when using ammonia-based solvents with brass core brushes plus, the nylon bristles are gentle on the rifling. .17 and .20 caliber brushes have 5-40 threads and can be used to get some of the benefits of the Copper Eliminator system with your existing small-caliber rod. The .22 caliber and larger brushes have 8-32 threads for use with most cleaning rods. Sold in 3 and 12 packs.
Big Book Catalog, Issue:68, Page:539
Sinclair, Issue:5A, Page:141