Optional Casters for Wire Shelving, Grip Ring Stem, 3" Wheel, Black, 4/Set (2 Locking)Wheels may be locked for stability.Using casters may reduce load capacity for the shelving unit. WARNING: This product can expose you to Di(2-ethylhexyl)phthalate (DEHP), which is known to the State of California to cause Cancer and Birth Defect/Reproductive Harm. For more information go to www.P65Warnings.ca.gov. - Cancer:Di(2-ethylhexyl)phthalate (DEHP);;Birth Defect/Reproductive Harm:Di(2-ethylhexyl)phthalate (DEHP)