I wanted wheels for hard floors for a chair Topstar already ordered from Amazon, but neither Amazon nor the seller of the wheels does not give details on the serial number for the wheels to order, so I did not know that they come in many models. Result: I found nonconforming to my chair. The vendor does not reimburse it refer prices (about 6) and wait to see whether I will receive a refund for the price of the product. Very disappointed!