how to make a thread on this face
Like as always...
I don't know which one you need, and you use SW earlier version
If metric - M90x1.5, M90x2, M90x3, M90x4, M90x6???
When you make 'Boss-Extrude5' - uncheck 'Merge result'
You'll get 2 bodies
Make spiral, e.g. for M90x2
Size of thread you can find in google, e.g. http://mdmetric.com/tech/M-thead%20600.htm
Now 'Combine' 2 bodies
And return your last 'Fillet9'
PS. Also needed the vanishing thread and the fillet at the ends of thread.