A spreader bar is a type of stabilizing component, used across many different applications. With industrial cranes, for example, spreader bars are used to distribute the weight of a load across more than one point. For that reason, they generally sit below the attachment hook on a crane. Not only does it decrease the load on a single point, but it also improves stability. In the case of a hammock or swing chair, it does precisely the same thing. The spreader bars distribute weight more evenly, which helps take some of the strain off the connection or hanging point but also makes the seating more balanced and stable. Needless to say, you want a hammock or swing chair to have at least one spreader bar below the main hookup. Traditional flat hammocks have two, one at each end.