These caster wheels are designed for chairs with stems that are fixed or welded to the base. This wheel accepts stems with dimensions of 3/8" diameter, up to 1.3" in length. You can select either hard or soft wheel treads. Soft treads are designed for hard floor surfaces like hardwood, linoleum, chair mats, and low pile carpet. Hard treads are suitable for most kinds of carpet. This product is offered in your choice of 4 or 5 pieces per set, specify your choice below. Specify a quantity (Qty) of 1 for 1 set.. 2 for 2 sets.. etc. Satisfaction guarantee, if product does not meet your needs, just return within 30 days for a refund (shipping is not refundable). If you have any questions, just call toll free.