The Hitch Adapters acts as a spacer to allow a flat mounting surface for the Steel Hitch (included with all current kid trailers). If your bicycle frame has a hooded dropout or some other obstacle that keeps the steel hitch from sitting flat against the frame, the Hitch Alt Adapter is required for safe trailer installation. The Hitch Adapters can also be used to extend the threading of your hub/axle if there is not enough threading to add the steel hitch. If your bike has a thru axle, you will need a replacement thru axle in order to use the steel hitch. To confirm the size needed, check the printed Thru Axle Fit Guide.