Does anyone know what size stem the original 2998 crown utilizes? I recently purchased what I believe to be an original 2998 crown (non-service crown) but am having a hard time figuring out which stem fits it. The current 1.0 mm stem doesn't fit the original crown as it only fits the service one previously.

 

I believe they should be 0.90mm

 

The thread on the original (non service) crown is larger than 1.0 mm.

 

Original stem for cal. 321 has 1.0mm tap. You got a wrong crown, unfortunately. It may fit stems for other movement though.

 

You sound like you have the crown with the 1.2mm thread width, you need two thread reducers to make it fit, 1.0mm -0.9mm then 0.9mm -1.2mm some works needs to be done but it is achievable.
Thanks Michael

 

Thanks Mike. I assume the crown I have is still a correct NOS for that watch?

 

It doesn't fit so it's not correct, but if it's 1.2mm and similar in size to the Speedmaster's crown and has the old logo then most likely it's for the 2914 Railmaster.