Fixed-gear rears are spaced 120mm and are ISO threaded on both sides for fixed gear cogs (1.37"x24tpi) and lockrings (1.29"x24tpi LH). 135mm-spaced rears are available as dual freewheel, with threading on both sides for single speed freewheels (1.37"x24tpi), and as fixed/free, with freewheel threading on one side and fixed-gear/lockring threading on the other. We now offer this fixed/free hub in a 120mm-spaced version, as well.