Another way to measure for the hub adapter is find an open ended wrench. Start with a 7/8" wench and slide over the middle part. You could use a metric wrench also and then convert to the nearest standard measurement. If the wrench fits without any play, then you need that size or a bit larger with the proper shims. After that, you should measure the inside width of the hub and compare with the dimension of the chosen adapter to see if you have enough room for chain Alignment.