One layer rack shelf with hook advanced technology design gives the suction sucker a stronger more powerful suction. mounts to most surfaces and easily removeable, mounting discs included for porous surfaces. easy to install with no drills, no mess and no fuss. one step installation easily removable exclusive surface warning indicator great holding power description advanced technology design gives the suction sucker a stronger more powerful suction. mounts to most surfaces and easily removeable, mounting discs included for porous surfaces. easy to install with no drills, no mess and no fuss. one step installation easily removable exclusive surface warning indicator great holding power