Park Tool Sliding Thru Axle Adapter - For PRS-20, PRS-21, and PRS-23 Converts any PRS-20 or PRS-21 to accept 15mm and 20mm thru axle wheeled bikes Use the axle from the fork to mount the bike to the Race Repair Stand PRS-20 or PRS-21 Also fits the PRS-23 one side is for 15mm axle the other side is for 20 mm thru axles