Metal back brushes are available in straight strips and coiled. Coils are available in open style or closed face, with the coils next to each other.
Straight strips are held in place by special holders. Coiled brushes are put on a metal shaft that turn due to mechanization. These are normally used to clean conveyors or items moving past the brush.
These brushes are made by putting bristles into a metal channel and folding it tight on the bristles, holding them in place. The size of the metal back is important to the construction of the brush.
#7 Channel is the most popular size