It is surprising that you would even bother buying their "kit". Just buy a wheel and bearing that match the existing inner wheel.
When you take it apart, you will notice that there are two sleeves -- a long one and a short one. Measure the thickness of the bearing and the length of the SHORT sleeve and SUBTRACT them from the length of the long sleeve --- cut here. Then measure the length of the SHORT sleeve and cut a piece that length out of the remaining part of the long sleeve.
Now assemble in this order: short sleeve, wheel, long sleeve, wheel, short sleeve.