We supply 1 of these 3 axles with all of our rear racks. The axle you need will depend on your bike.
Single Thru Axle
Modern bikes use thru axles, select the single thru axle if you know your pitch thread.
Universal Thru Axle
Ships with multiple thru axles to fit all bikes
Quick Release Axle
Usually found on older bikes and are usually hollow with a lever on one side.