Replacing a broken A7750 stem, which size

[stxtf]

So I accidentally broke my stem on an AP 7750 sec@12 movement. Looking at replacements online shows me different kinds of stems- tap 10, tap 8, tap 6. Which one should I get?

 

[AstroAvia]

You should measure the size of the square cross section of the stem, for that is where the "tap" size comes from.

 

[KBH]

The tap size comes from the threads on the crown end. Most reps are tap 10.