The breech plug body fits all Knight DISC Elite and DISC Extreme muzzleloaders. It does not fit the Knight Mountaineer or Ultralight. The breech plug body is made from 17-4 stainless heat treated to H900 providing the ultimate in strength and corrosion resistance. The body comes with one vent liner, part number VL-1, installed. Additional vent liners are available in packs of four.