 If a solvent-weld cap is used to provide for a future connection point, several inches of pipe must be left before the cap; when the cap is cut off for the future connection, enough pipe must remain to allow a new fitting to be glued onto it.A plug fits inside the pipe segment or fitting.A barb (or hose barb), which connects flexible hose or tubing to pipes, typically has a male-threaded end which mates with female threads.