If they all have holes in the centre DO NOT GLUE THEM TOGETHER
If half of them are solid then once you have pushed the axle through the inner roller you can glue the outer to it<
If all the rollers have holes in them then pass the axle through both the outer and then the inner roller then into the hole in the hull and locate the axle in position,
The outer roller will have a sunken centre around the hole for the shoulder of the axle to sit, The inner will just have a plain hole.
Do ensure that both the inner and outer rollers on the axle can turn independently.
If you have a choice of rollers and the axles are long enough and have a shoulder then go for the hollow ones because they run more freely.
