The pair on my UO-8 is missing one outer nut, so I am running half-step gearing w/ no locknut on the front shifter. I have had no issues w/ unintended downshifts. Another option for those missing the locknut and experiencing loosening would be Loctite on the hex nut, although I have not had to resort to this. I do use Loctite on Italian and French fixed BB cups, however.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069