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Or, if you have a large-ish socket set, you can use two sockets, that are slightly smaller than the bearing, as drifts, to tap them in with a hammer.
Most important thing is to ensure that whatever you use as a drift ONLY comes into contact with the outer race (hence the suggestion of using the old bearings).
Using the axle alone would press against the inner race, and most likely knacker the bearing.
What's the best way to fit them, can I just use the axle the press them in?