Bead lock, otherwise called bead wedge is a very helpful pool liner installation accessory that comes in handy when replacing a Beaded pool liner. It is a long rubbery piece that can help to keep the beaded lip of the pool liner in the track called bead receiver. This one is a must when you replace a beaded liner because it is fairly inexpensive and one of the common faults of beaded liners for above ground pools is that they have a greater and greater tendency over time to pop out of the track. Anything that can stimy this problem will be greatly appreciated in the future. Preventing problems that can happen is the mark of a true professional, or at least of a smart pool owner.