I just bought a 40tooth Sprocket Hub Adapter off of Ebay from Gasbikedotnet for 58.99 for my cruiser. They get more expensive the more teeth you get on the sprocket. From what Im seeing most cruiser hubs are measuring in around 1.51 and thats for coaster break hubs. To be sure measure your hub with calipers or you can do the string measurement. Wrap string around your hub then measure what the length was and divide by PI which is 3.14. That is the size i got and it fits my Schwinn Swindler and it should fit my 2nd build which will be a Genesis Onyx cruiser. Now you can order the same one from kingsmotorbikes.com for a bit cheaper and they are the same seller.
Will