There are three concerns when matching 6-speed hubs.
1) Are both freewheels in question ISO-threaded? (Probably yes, in this instance.)
2) Are both freewheels standard-spaced, or are both freewheels "ultra"-spaced? (If one is standard and the other is ultra, you may need to adjust wheel dish and axle spacers.)
3) Do both freewheels have low gear (large) cogs within your rear derailleur's capacity?
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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