I have just a few prototype units of my sprocket adapters left. These are what I consider the standard size which is a 40t sprocket with the adapter sized for a Shimano 110 hub. $80 plus shipping. These are perfectly balanced, offer greater clamping force and do not interfer with the hubs brake arm. I will also have more in two weeks.
DSC06212 by Sportsman Flyer, on Flickr
DSC06212 by Sportsman Flyer, on Flickr