Savar in Hindi means rider and in this case, one of the beads rides — essentially a one mukhi — over the other bead, which can be of any mulch. In a Savar rudraksha, one of the beads will always be a one mukhi and it is considered to be next only to the original and rare one mukhi round rudraksha in virtues. Some people even cut the one mukhi rudraksha from the twin bead and use it separately. However, experts feel this will not be a pure one mukhi rudraksha. Natural holes exist in both the beads.
Mantra : Om Namah Shivaya
References : Kamal N Seetha (2014) The Power Of Rudraksha