Sometimes you need to find the sweet spot to keep a bead on, sometimes the size is just off. Once the hair starts looping a little, they stay in easier. Like Soaring Eagle said, find a thinner bead or larger dread. For thinner beads, go to a thrift store, buy a wooden necklace and take it apart for the beads, if it needs a slightly larger hole, just hand drill it. A good tip for putting on beads is to use dental floss: put both ends through the bead and form a loop, put dread in loop and then very gently pull hair through the bead. If it feels like too much hair at first, since it is kind of doubled over when looped in the floss, just go lower on the dread where it is thinner. Once the bead is on, just move it up higher if needed. This is by far the easiest way I have found. Happy Dreading & Cheers,

make sure the beads the right fit slide u]=it up till it gets tight then pull the dread while pushinjg it up til its firmly seatted and wont budge

if it slips down find a thicker dread or thinner bead