Altech Cylindrical sensors are available
  in diameters ranging from
  4mm (.16 in.) to 30mm (1.18 in.)
  with sensing distances up to 40mm
  (1.57 in.). Most models feature nickel
  plated brass (BN) housing, but
  stainless steel (SS) and non-metallic
  versions are available. Both flush
  mount and non-flush mount sensors
  are available. Flush mount versions
  are often called shielded or embeddable.
  Non-flush mount sensors are
  also called non-shielded or nonembeddable.
  Non-flush sensors
  have larger sensing distances than
  their flush mount counterparts. All
  Inductive sensors meet IP67
  (NEMA1, 3, 4, 6, 12, 13) protection
  levels. Please refer to pages
  132-133 of this catalog for more
  information.
  FLUSH MOUNT