text: In plumbing, an adapter is generally a fitting that interfaces two different parts. The term commonly refers to:
  *any fitting that connects pipes of different materials, including:
  **expansion adapters which have a flexible section to absorb expansion or contraction from two dissimilar pipe materials
  **mechanical joint (MJ) adapters for joining polyethylene pipe to another material
  **bell adapters which are like mechanical joint adapters but contain a stainless steel backup ring to maintain a positive seal against the mating flange
  **flange adapters which attach to a polyethylene pipe with butt fusion to stiffen a junction and allow another flanged pipe or fitting to be bolted on
  *a fitting that connects pipes of different diameters, genders, or threads 
  **adapter spools (also called crossover spools), used on oilfields and pressure control, have different diameters, pressure ratings or designs at each end
  **adapters to convert NPT to BSP pipe threads are available
  *a fitting that connects threaded and non-threaded pipe