Can anyone tell me how I can find the part number for an Omega watch stem please.

I might be able to help if you know the calibre?

Thanks Dave, it's a Cal 620

Mike,
My Bestfit catalog shows Omega part number 401/509.

And also shows a WP stem number 360/330.

(for calibre 620)

http://www.ofrei.com/page1041.html

scroll down a ways and you'll see it listed here.

check cousins as you are in UK might be better on shipping for one part.
https://www.cousinsuk.com/cate.../watch-parts-branded

Thank you all. Very much appreciated.

I know what I'm looking for now.

Getting there slowly.

Mike