There are non center cutting end mills that have a hollow in the center, but it is quite shallow and small diameter on one as small as 3/16". They are seen on 4 flute cutters, not on 2 flute. Not sure of your purpose...
There are single size hollow end mills, usually special and pricey, I suppose. And without supposing, there are adjustable hollow mills, but they are definitely expensive. (eBay may be a decent source)
Then there are regular wood plug cutters, which can work on aluminum and other metals without modification, and possibly steel if the tooth shape is altered by grinding or by hand with a diamond pocket hone. And, lastly ( for me at the moment) there are countersinks with interchangeable pilots, one of which might suit your purpose with the pilot removed.
Do a Google image search for hollow end mills and you'll get some ideas.
Thanks for the replies. Work got in the way for a few days so delayed here.
The reason for the hollow end mill is to round the rectangular portion of the top hole on the piece pictured. The top section rides in the 3/16" slots I make on another piece.
I figured it would be much quicker and easier for me to mill the top section round after drilling the hole. Just a quick end mill change.
Higgite, correct, basically a hollowed out end mill with a 3/16" ID. As long as it fits into one of my 2MT collects then I'm good.
The reason why I want to go tjhis approach is because it is so much quicker and easier while the pieces are set up for drilling, to just change the chuck with a collect/hollow end mill and perform the outr diameter cut.
The piece picture is made with five others all on the same piece of bar. I make all the hole cuts, taps and all and then I just cut them to separate them and they're done.
Boring and all the other suggestions I really don't understand, but they sound like a lot more set up than what should be needed.
Let me rephrase the original question.
Can an end mill, say a 3/8" or 1/2" end mill be hollowed out to have a 3/16" ID without destroying the end of the end mill bit sharpness?
If so, maybe I could pay somebody to just make me one of these.
Lastly, the depth of cut I need is only .60".
I don't think so. As long as the end of the end mill cuts then it should remove the surrounding brass as the bit descends into the piece, with the .60" protrusion I want asending into the 3/16" hollow interior of the end mill.