Most decent mountain bikes these days come with 15mm through-axles up front. You have two options for mounting to a SeaSucker rack: use a somewhat-more-expensive Fork Up adapter, or use their dedicated 15/100mm fork mount. The 15mm fork mount is bolt-on, meant for riders who are always using their rack with their thru-axle bike. According to Seasucker's friend and MTB pro Macky Franklin: “The 15mm fork mount is perfect. So much steadier than using the adaptor.” If you’ve got a Boost front hub (15/110mm), make sure to get one of Seasucker's Boost Adapters (sold separately) to get the fit right.