..so you think any old rollerblade bearing will fit your hubs? Good luck with that.
Go to spinergy's site and read through the tech sheets to find the 4 digit cartridge number. Formula uses #6000 (10 x 26 x 8). 90% of bicycle cartridges come from here: http://www.endurobearings.com/produc..._bearings.html

as I posted before look at the ceramics if you want an improvement.

*edit*
the formula bearings are designated with a LB shield, which, as far as I can tell only uses a shield on one side of the bearing. must be so they roll with less drag.