Adapter is needed to connect two fibre optic connectors. Adapters are different by construction and function.
Connection adapter is needed to connect same type of connectors, switching adapter when connecting different types of connectors. Adapters are available in Simplex, Duplex or Quad versions and with plastic or metal housings. Single mode (SM) adapters sleeve material is Zirconia, multimode (MM) sleeve material is PhBr.