The Sensor sheath is made of metal, usually stainless streel (Hastelloy or Inconel is used for certain high temperature applications), and typically contains 2, 4, 6 or 8 conductors connecting the sensing element to the lead wire. A single T/C requires two leads, while a duel T/C requires four, leads. A single resistance temperature detector can have two, three, or four lead, and a duel resistance temperature detector can have four, six, or eight leads. The sensors from moisture and corrosive and/or abrasive process conditions and helps to shield the signal from electrical noise. To insulate the conductors from each other and from the sheath, the sheath is filled with a compacted finely powdered insulating packing material, typically magnesium oxide or aluminum oxide, which surrounds the sensing element and conductors.