Technical question regarding stem/crown/case...

Kind gents, and that occasional female watchmaker:

Below you will see two pics: the first is a movement shot which shows the crown and stem, and the question I have concerns that little collar right below the crown. Most dust-proof crowns apparently do not have this, but it was needed here because of the corresponding little tunnel in the case, that you can see in the second shot.

So my question is, if the crown ever needed replacement (originals are a nearly impossible find), would I have to have a little collar machined to sit right below the new crown, and would it have to be afixed to that crown, or is unaffixed okay, where it just acts like a case spacer? Many thanks.

The post on the crown is where the stem threads into. All crowns have them. The length is not really important, as the crown will seat on the case tube...

Thank you, Al. That's much appreciated.

Al, a follow-up, if I may. The post on dust-proof crowns: are they all pretty much the same OD, so that they would all fit any case they were mated to? The reason I ask, is that it seems that the little tunnel in the case has to catch at least some of the post on the crown, otherwise the stem would wiggle a bit? Thanks again.

The diameter if the post will depend somewhat on tap size, so you would need to make sure it will fit inside the hole in the case tube certainly. But typically it's the ID of the crown that both seals and locates on the OD of the case tube. The post in the crown really doesn't come into play in most cases.

There are some designs where the post is a sealing surface with an O-ring that is located inside the case tube - Rolex for example uses this design on some of their watches certainly.



But most times the post has clearance and is not a factor with regards to sealing or locating anything...

Excellent, thanks very much.