When sourcing ESD wheels, the most critical specification is surface resistivity, which should typically range between 10^3 to 10^9 ohms to ensure effective grounding. You must also evaluate the load capacity per wheel, ensuring a safety factor of at least 1.3x the expected load to account for uneven floors. Material choice is vital: Conductive Polyurethane (PU) offers excellent floor protection and durability, while Conductive Rubber provides better grip and noise reduction. Additionally, verify the bearing type (e.g., precision ball bearings) to ensure low rolling resistance in cleanroom or assembly line environments.