Blind disks are officially known as Flange covers, and some are also called Blind flanges or Pipe plugs. They are flanges without holes in the center, used for blocking pipe openings. They serve the same function as caps and pipe ends, but the blind disk seal is a removable sealing device, whereas the seal of the cap is not intended to be opened again. There are various types of sealing surfaces, including flat, convex, concave-convex, tenon-groove, and ring-connected surfaces. Materials include carbon steel, stainless steel, alloy steel, copper, aluminum, PVC, and PPR.