oops . . . .sorry . . . . .
the hardware store ball bearings were too big . . . .. I had choices, either buy the right size freom McMaster-Carr (or similar), and get 500 of em, or slightly widen the plastic groove into which the bearing has to fit in the switch housing . . . . 5 minutes with a small file, and, hey, presto, work fine with an oversized ball bearing ;-}