Just curious: originally, the 7912 came with either no. 4 or no. 6 end-links, yes? If that is true, then the link width just before each end-piece should be the same, regardless if it came with either width end, right?

Or, is this completely wrong, and the bracelets have a different width ends, and in fact, different taper widths as the bracelet approaches the end-links?

 

7912 bracelet's always have a last link of 18mm. The endlinks decide on to which watch it will fit.

 

So the 7912 has 18mm wide ends and that is always the same. Their difference is in the end links. The 4's are 18mm and the 6's are 19mm.
Happened to have these handy so took some pictures. You can see the difference well. The 4's are a much nicer fit on the 7912.

 

Thank you both for clarifying.