My ~85 bianchi (italian) track bike takes 26.8. Don't know if that is the spec for their 80s track bikes, italian bikes, or both.
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1989 Schwinn Paramount OS
1980 Mclean/Silk Hope Sport Touring
1983 Bianchi pista
1976 Fuji Feather track
1979 raleigh track
"I've consulted my sources and I'm pretty sure your derailleur does not exist"