wheel.
push the dowel in from the other side until it reaches the plug and mark the place where the dowel just comes out of the other spool.
then pull out the dowel a bit and cut the dowel about 1/8" inside that mark.
push the dowel back in and plug that second side side with a wood plug.
now that you have the right fit, slide each wheel off the dowel one at a time and put some glue into the open end of the spool, put the wheel back on the dowel and twist around one of two times to help the glue connect to both the spool inside and the dowel.
screw 