Shimano Single-Speed / BMX Freewheel <br /><br />Single-Speed/BMX freewheel<br /><span>Designed for 1/8 in. chains only</span><br />1.37 in. x 24tpi (English) mounting threads<br />Available in 16t, 18t and 20t ONLY<br /><br />USES SHIMANO TL FW-40 Tool - sold separately