Completely nonsensical. These brushes are very light and soft in thickness. I bought these to clean the valve covers inside and out on my truck when I removed them. I could understand that they are not ideal for clearing up the dark years. but they have no strength and bow at once. I've had better luck using a toothbrush and a brass brush from the gun cleaning kit for all the work, although they were completely clogged with dirt they worked better. To be honest, I'll probably throw these out. I really don't see what use they can bring. Useless.