Not sure which hub came on your bike, but if you got a set of calipers you could measure the hub diameter and have a better way to compare... these things need to fit exactly so accurate measuring is a must. Now if you can see or find a name brand and/or part number on your hub it would be a lot easier to match up...
Several places offer these adapters in several different sizes so there shouldn't be a problem finding one that fits... some places will even make a custom one if they don't carry the right size... Hope this helps.