As it seems to happen every couple of years, the powers that be have chosen a new fork mount standard encourage the purchase of new, "better" bikes: 12mm. These new through-axles are showing up on high end road and 'cross bikes now. Are we witnessing the demise of the venerable 9mm quick release? Only time will tell.
You have two options for mounting a 12mm fork to a SeaSucker rack: use a somewhat-more-expensive Fork Up adapter, or use our dedicated 12/100mm fork mount. The 12mm fork mount is bolt-on, meant for riders who are always using their rack with their thru-axle bike.