I have a set of Ofmega sealed cartridge bearing hubs. Ofmega made the Avocet sealed cartridge hubs. The bearings in my Ofmega rear hub are the same size as in the front hub. They are industry size code 6001. 12X28X8 mm. Two rubber seals. You can find them on ebay if you search the generic specs.
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My C&V Bikes:
1972 Bottecchia Professional, 1972 Legnano Olympiade Record,
1982 Colnago Super, 1987 Bottecchia Team C-Record,
1988 Pinarello Montello, 1990 Masi Nuova Strada Super Record,
1995 Bianchi Campione d'Italia, 1995 DeBernardi Thron