2. Marking: If the mark on the figure-8 blind plate will be written as "M" or "B", where "M" means through-flow blind plate and "B" means fully closed blind plate.
3. Symmetry of blind plate: If the figure 8 blind plate is highly symmetrical on the drawing, it is a cross-flow blind plate; If the blind plate has no symmetry, it is a blind plate.
4. Whether there are connecting holes: if there are clips or connecting holes with screws on the 8-shaped blind plate, it is a cross-flow blind plate; If there is no such hole or clip, it is a blind plate.