Some use slotted steel to adjust the axles others ensure they are 'square/plumb' during the build. Do a you tube search as there are tons of mill there and lots of them have close-up shots that give their 'secrets' away. LOL. The roller bed can be anything from steel skate wheels to inline/roller blade wheels. The bearings go from ABEC-5 and ABEC-7 all the way to the really expensive ceramic bearings. Hit up inline skates on ebay and you can buy in bulk for $$$$ savings. EWO