These sit inside the wheel, allowing them to spin. You will need 4 in total, 2 in each wheel. The majority of scooter wheels actually come with bearings pre-installed. When preinstalled there is also a spacer installed between the two bearings, this is to stop the bearings being squashed by overtightening of axles.
But what ever you do, bearings will wear out, they are a consumable item. It could take months, weeks, days or hours to damage wheel bearings, it really depends on the impacts its received. Wheel bearings are the easiest thing on a scooter to break and that’s simply because sideways impacts break bearings.
New wheel bearings are best fitted with a press (we can do this instore at Numfish for free). Any other way of installing bearings is prone to damage the bearings whilst installing them. We also give the option to customers regarding the installation of the bearing spacers, because aftermarket fitment usually results in noise of the spacer rattling around.