All bearings have a universal identifier number on them and often a four digit number. For example 6304. Just take these numbers or preferably the bearing to the supply house and get the new ones.
Now the difficult part. There are grades of the same bearing, from utility to the uber expensive submarine grade. Just get them a couple grades better than utility and you'll be fine. Wheel, transmission etc., are an easy match for a lot less money than Mussolini charges.
Then there is open, shielded and sealed but that's an easy call.
*One exception is the outrageously expensive Duc crank main bearings. Although you can match them up for half the price, don't. The Duc spec bearings have a slightly different thrust angle to them that works. Although identical in appearance to the off the shelf pieces these generics will prematurely fail.
