On the SK website go to Order a catalog and down load the PDF
It has all the sizes of every socket.
I’ll try to post the page here.
https://sktools.com/content/dam/sktools/catalogs/SK%20Catalog%202018%20Full.pdf
This is the only one I’m not sure of now.
It looks like a small press to remove something off a shaft. Looks to be a pretty specific tool. The stamp inside says. Z103
Any ideas?