The topeak two up third hook comes in two types of mount bracket an upper or a lower bracket this will determine where about on the two up stand where you can mount the bracket and thus store your bike on your two up stand you are able to store up to 4 bikes in total and so these add on hooks are great if you already keep 2 bikes on your stand and need additional room the topeak third hook can be adjusted 30 degrees from horizontal fitting sloping top tubes topeak about the brand topeak is