From "Definitions of Markings" at the end of the article "The Campagnolo Bottom Bracket" in Campagnolo Record News Vol 1 No. 2 Winter 1982-83, bottom of page 7 (second of two pages of charts explaining the different markings and dimensions of various BB axles):
F. "SL", "Z" may be found on some old axles. They were production codes and have no significance in identification.
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No significance as to purpose, perhaps, but if the markings truly had "no significance", why mark them with those markings at all? ;-)
Lee Berg Palo Alto, CA
Stephen Barner wrote:
> Anyone know what the Z on a Campy 68-SS-120 BB spindle was supposed to
> indicate? I have seen it on spindles for both thin and thick, rifled cups
> dating back to the early '70s, so it doesn't have anything to do with the
> CPSC mandated changes in '78. I notice that the crankarm does not go quite
> as far onto a "Z" spindle that I have, vs the same spindle without the Z,
> though this could be just due to manufacturing tolerances. It doesn't seem
> to have anything to do with length, flange spacing or offset. Can't be
> absolutely sure if I've seen it on a triple spindle, but I believe I have.
>
> I cannot find anything on this in the archives or usual places.
>
> Steve Barner, Bolton, Vermont