Product details:

They feature 1/4 in. steel plate construction with rock-hard, non-marring, poly ball-bearing casters. The dollies are available in a standard-duty version, supporting 6,000 lbs. per set, and a heavy-duty version, supporting 10,000 lbs. per set, and they are also available in 8 in., 12 in., and 16 in. widths.