Various options. These axles are not compatible with pre 2012 X-hubs. They fit X- hubs for disc brakes.
1) QR15 - converts a Q/R X-hub (disc) to 100x15 thru axle
2) Q/R front - converts 100x12mm or 100x15mm hub to Q/R
3) Q/R rear - converts 142x12mm thru axle to standard Q/R
4) X-12 rear - converts standard Q/R to 142x12mm
5) RS-1 front - converts 100x15mm to RS-1
6) 100x12 - converts Q/R to 100x12mm