Offset Tungsten Beads aka Jig Off, Inst Jig tungsten beads are very new in most fly tying circles. The shape is more like a tear drop with an eccentric hole which helps the fly to act like a jig style fly, even if the hook is a standard shank nymph or streamer hook and not a jig style hook.
These beads are heavier for their size than slotted beads as well.