The large bead on the strand is symbolic of the wisdom that allows one to recognize emptiness (sunyata) and the bell-shaped bead surmounting it is symbolic of emptiness itself. The bell is recurring symbol for emptiness in Buddhist ritual, its ringing being the sound of emptiness made reality.
A few words on Buddhist philosophy: “emptiness” means that, despite appearances, everything one encounters in life is absent of absolute identity, permanence or an in-dwelling absolute “self” (anatta). All things are connected and mutually dependent, in a constant state of flux, transforming and becoming (rather than self-centered and fixed). Only when the abandonment of self occurs can the transcendent state of enlightenment be achieved.