Can you help with the name of this wheel, please?

Hello all....First thread as I now embark on this exciting watch repair hobby.
I have had some luck with my1966 Seamaster 166.003 in repairing the keyless works, calibre 565.
This is the first time I have stripped the watch down and I intend to strip it down further for a full service as I am learning this watch making/repairing hobby.
In the meantime, whilst fixing my keyless works, I have managed to lose one of the smaller wheels. It flicked off my work area, never to be seen again, as I'm sure many fellow enthusiasts have experienced.....Lesson learned.
Can anyone help me with naming the actual wheel that I have circled in my picture? Or better still, does anyone know the part number, or where I can find it?
Thanks in advance.....Looking forward to delving deeper into my Omegas.
I also have a fantastic 1973 Geneve that was my father's 25 years of service Gold Watch which is in immaculate condition

Thank you so much Archer. That info led me to be able to order a replacement and be sure it is the correct part. It's coming from Italy and I'm in Australia so I'll post an update when I get it all back together......Thanks again.