Breakthrough Clean Technologies, Double Ended, Flexible Nylon Brush California Prop 65 WARNING. These products contain a chemical known to the state of California to cause cancer, birth defects and other reproductive harm. Lead: Cas-No. 7439-92-1 Flexible Double Sided Gray Product Description This flexible, double-ended utility brush gives you the versatility you need when cleaning fresh carbon or powder residue off your gun without scratching your firearm's finish.