The classification of Rudraksha is defined by the number of clefts (the vertical lines) on its surface. These clefts are also known as "Mukhis."
A particular Mukhi rudraksha corresponds to the effects of a certain planet. If a particular planet is weak in the horoscope, the Rudraksha stimulates its qualities. On a planet being too strong or malefic in the chart, the rudraksha channelises its influence in a positive energy. A thorough checkup of the horoscope must be done to select the appropriate rudraksha. Since none of the rudraksha gives a harmful effect, hence there is no possibility of risk taking.
Still, general categorization of its properties and the attributes to which different Mukhi rudraksha relates to are described over here.