Convertible hubs means you can run different type of front axles without replacing the hub or the fork by way of an adapter. The hub itself is a Thru-axle 20mm diameter and it comes with an adapter that allows you to use standard 9mm Quick Release skewers. Also available to be purchased seperately is a 15mm TA that will allow you to use the front hub with a fork that is equipped with 15mm TA. What it boils down to is for the rider to be able to use one wheelset with variety of forks to his/her liking without purchasing a separate hubs for each let alone a full wheelset.