Is that a monocoque case? If so the stem should be a two parts one. Is it missing as well?
To be sure of the reference, it would be better to see the back of the case. Do you have any pic of it?
Here you are. Note that there are several kinds of split (two parts) stem, the pic in the link above only shows one of them. But they are all more or less like that.
https://www.google.fr/amp/s/forums.watchuseek.com/f20/where-find-seamaster-part-how-called-3504410.html?amp=1
Here you are. Note that there are several kinds of split (two parts) stem, the pic in the link above only shows one of them. But they are all more or less like that.
https://www.google.fr/amp/s/forums.watchuseek.com/f20/where-find-seamaster-part-how-called-3504410.html?amp=1
