This lead mounting system is one of the best & most practical systems we have found for the well documented rotten bottom rig. Survives hard casts but releases the lead every time when necessary. Sold in packets of 8. Many ideas & systems have been used in the past for effectively releasing the lead in a tangle but few have been as successful as this rock release mechanism which is basically a refinement of these existing ideas. Not only practical to rig without the need for fiddly pins but it has never failed for us yet.