These caster wheels are sold as sets of 5. They are a standard size that will fit many typical office chairs, stools, etc. The upper nylon barrel ("neck") is a visual aspect that is usually matched to the width of chair legs or chair base style. The barrel is available in several diameters, you specify below. The top metal stem is a standard 7/8" long. The stem diameter is a standard 7/16" thick. The wheel diameter is 2". These wheels have a hard nylon tread which is recommended for most kinds of carpet, but not recommended for hard surface floors. Satisfaction guaranteed, 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.