This thru axle allows you to adapt your bike to the Smart ZPro roller if you have a 12 mm rear hub. The thru axle is a device that crosses the entire hub of the bike from one side to the other and is screwed on the other side. At ZYCLE we have 7 models of axles available which vary according to the length and thread pitch of the fastener. Please note that the choice of the type of fastener to use with your ZYCLE roller depends on the diameter and length of the axle fitted to the rear wheel of your bicycle.