These "Grapple" leads are designed to allow for extremely detailed mapping of the seabed. Their tips allow you to identify features on the bottom that would go unnoticed with a smooth-surfaced lead.
The system works by locking the four points in a vertical position before casting and feeling the impact with the bottom as usual. As you retrieve the line, any algae, debris, or natural food sources (such as mites) will become entangled around the lead, helping you understand the nature of the bottom.
If the lead becomes stuck due to excessive algae, rocks, or mussel beds, simply apply constant pressure to unblock the tips and retrieve the equipment normally.
They are sold in packs of two and are available in 2, 3 and 4 ounce sizes.