The Rosary of the Seven Sorrows, also known as the Chaplet of Seven Sorrows or the Servite Rosary, is a Rosary based prayer that originated with the Servite Order. It is often said in connection with the Seven Sorrows of Mary.
It is a rosary consisting of a ring of seven groups of seven beads separated by a small medal depicting one of the sorrows of Mary, or a single bead. A further series of three beads and a medal are also attached to the chain (before the first “sorrow”) and these are dedicated to prayer in honour of Mary’s Tears, as well as to indicate the beginning of the chaplet. Conventionally the beads are of black wood or some other black material indicating sorrow.

Sharon at Swords of Truth explains:  Rosary of the Seven Sorrows