Most vintage 1960s/early 1970s bikes used #35 chain. But with torque converter they seemed to move to #41 chain (bigger). But Speedway and a few other makers used #40 chain (same pitch as #41, but wider and much stronger.) #35 chain is really pretty wimpy, i personally try to not use it. And #35 is not an actual roller chain, where #4x is. #41 is a lot better (though technically not really stronger than #35), with #40 being the best of the group. But obviously you use what your sprockets are pitched to use. On the newer Chinese bikes i'm not really sure what they use.