Burley Ballz Thru Axle: 12 x 1.75 177mm. Burley Coho Axles Enables connection of the Coho XC trailer to bikes with 12mm rear thru axles. Multiple thread pitches and lengths available. Stock thru axles are not able to accommodate any sort of axle mounted hitch system. A Burley Coho Ballz Thru Axle is required for any bike with a 12mm rear thru axle to use the Coho XC. The Burley Ballz Thru Axle is not compatible with all carbon fiber bike frames (consult manual).