that could be french, my zeus is like that and it is french threaded. But so is my Mclean, and it is english threaded. Try screwing an english locknut (gently) and back it off if it doesn't screw on easily. Velo Orange has a cheap french headset, it's pretty plain but works fine on my zeus.
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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"