Burley’s official adapter for bikes with a 12mm thru axle. Stock thru axles are not able to accommodate any sort of axle mounted hitch system. The Burley Thru Axle is a requirement for any axle mounted hitch system with a bike that has a 12mm thru axle. These Thru Axles have an external male threading on the end to accommodate the installation of a axle mounted hitch system.