The screw-in design of these fittings makes it simple to install or replace one, and they create a tight seal without any necessary adhesive. Plugs contain a male end to screw tightly into the end of the fitting they are sealing, thus preventing fluids from leaking out of the system. This means they work well in situations where they might need to be removed to change the configuration of the system, add a line or change the overall design. This level of flexibility makes plugs a popular way to seal a PVC system. Plugs are also available in spigot style ends that glue into a slip style fitting end.