Bill Noble writes:

MSKNR-10CA-3 the R of course means right handed, I was able to
decode some of the rest of the part number, but it isnt' at all
obvious why they have the little special set screw in the back nor the
oval hole in the middle. Do these go on boring bars? a special
"mother" holder? or what?/?/?

Page B44 in the Valenite June 2007 Turning Tools print catalog.

It's a 75 degree lead facing tool. That is, about all this is good for is
facing ends of stock in a lathe.

Takes square inserts in the SNxx style, seems like the 322 size.

Maybe the set screw in the back was added to plug a coolant passage option?
This feature doesn't appear in the catalog, but neither does the "CA" in
the designation.