There is a three-holed bead besides the 108 beads, which is called Master Bead and tower, also called Guru.
From the above picture, you will see what is a "Guru". A guru bead can be the same materal with the 108 beads, or different materials. Generally speaking, the "Guru bead" should be larger than the 108 beads.
Now in the Tibet, most Tibetan prayers do not pass over the guru bead, nstead theyreverse direction by turning the mala around, and starting a new circuit of 100, going back the way they came. We are not sure, honestly, why people do this, and they just do it out of habit rather than for any special reason. (We are told some people believe that if you continue in the same direction and cross over the guru bead, it is like stepping over your teacher.)
We have various types of Mala's Guru Beads for selection. Please check here to see if you can find any guru beads you want.