Metric bearings at least are available with built-in rubber seals and well worth considering.
They are the same overall size as the regular bearings, come “sealed for life” with the correct quantity and type of grease – basically “fit and forget”.
The bearings are identified by a RS or 2RS suffix, (one or two seals), these should not be confused with shielded bearings which carry metal protective covers that do not completely seal the bearing.
I have had bearings of this type in a Moto Rumi for over 20 years with no hint of trouble.
