Crowd control
Crowd control barricades are sometimes placed side by side without being attached, but they are most effective when they are hooked together. Without a solid interlock, barriers can be lifted out of place by individuals in a crowd, compromising the integrity of a line. The most popular hook style is the "classic" style in which the male hooks are 15 inches apart. The second most common, the "wide hook" style, has the male hooks 25 inches apart.