2- Docking Disc (photo shows both front and back of the disc)
Docking Disc are designed to attach to the back of the chair. Then you place you suction cup to flat part of the disc.
Docking Disc are needed for chair surfaces that my be rough and not smooth and flat.
YOU MUST LET DISC SIT 24 to 32 hours prior to placing your any A~flexX Assist Arm.