These are adapters to use on a bike with a one piece crank which uses pedals that have a 1/2" spindle. By threading these into the crank, it allows user to install pedals that have a 9/16" spindle. There are a lot more choices of 9/16" pedals on the market to choose from. The 1/2" pedals are generally a lower quality than what is available in 9/16" pedals. These can also be used to move the pedals away from a one piece crank so your heel doesn't hit the crank arm. The pair includes one left (left hand threads) and one right (right hand threads)