These are used to keep track of accumulations of mantras and practice... One side is used to count 1 full round of the mala beads.....each bead representing 100 recitations.  The other side keeps track of 1000 counts,

They are attached to a mala via a slip knot one on each side....one counter has a bell and the other counter has a vajra to distinguish them from each other.  Also symbolic of always having one Bell and Dorje (Vajra) with you at all times...