PVC(Polyvinyl chloride) fittings are used to connect sections of pipes or tubes, adapt to different sizes or shapes, and controlling the flow of water. There are two predominant types of PVC fittings namely PVC Glue Fittings and PVC Threaded Fittings. The difference between the two is that PVC Glue Fittings result in permanent joints and PVC Threaded Fittings are semi-permanent and can be replaced. PVC Glue fittings are joined with primer and cement- a chemical solvent that melts the surface of the PVC and then quickly re-hardens to fuse the pieces together. This results in an airtight, leak-proof bond similar to what you get with welding metal. An example of such a fitting is a PVC Glue Reducing Socket which is used to join together two pieces of PVC pipes with different diameters. Another example would be a 90 Degree Elbow which is used to connect two pipes of the same diameter at an angle of 90 degrees.PVC Threaded fittings utilise a simple threaded connection whereby replaceable 'male threaded' are screwed into 'female threaded'.Male threads have a thread on the outside of the fitting and female threads have a thread on the inside. When you thread the fitting in, it compresses against the other threads.PTFE tape is used to thread these together and the proper way to assemble threaded fittings is to finger tighten, then add one to two turns but no more. An example of a threaded fitting is a Reducing Nipple Male Threaded which is used to connect between two female threads of different diameters.