Step 7: Axle
The sleeves that go over the axle in both ends is made from a carbon fibre tube, that i had from an old kite, and it happened to fit perfectly. Make sure these also are more than the 3mm tall that it is going to end up as, it is way easier to remove that create material.
It is also a good idea to drill the holes in the slides that the axle are going to sit in by now. That way you can test the fit, and make sure you don't make a too small axle. You want a close but free running fit.