I have a lot of people contact me wondering why they can't just screw a 24-6020 tube into a rep case so they can use a Rolex crown. It sounds like such an easy process, anybody should be able to do it! Not quite so simple, though...
Most rep cases have a tube hole that's too small so it will need to be drilled out and re-tapped:
A lot of folks do this and are bummed when the crown sticks up like a third-eye zit! Most people don't look at the new tube that closely and fail to notice the chamfer/angle between the tube's crown threads and case threads so they keep cranking on it until the tube snaps off in the case:
I have quite a few sent to me in this condition...
It seems all that would be necessary would be to countersink the tube hole to allow the tube to set flush against the case:
Well, not quite - crown still sticks out too far:
The amount of countersink is dependent on the crown being used so from this point I just increase the countersink into a shallow "counterbore" untill the crown sits about the way I want it. The amount of counterbore will vary so I'm not going to say how deep, that is something you have to experiment with to find:
Screw the tube in, just right:
And you're all set!