These are used to connect an appliance that uses a disposable cylinder, or a Coleman or Primus Campstove hose, that uses a disposable cylinder to a bulk tank.
Stock number #BP4122 has a 5' hose and hand wheel for easy connections. The #BP3122 has a 5' hose but is designed to be tightened with a wrench. The #BP3123 and BP4123 have 12' long hoses.