large slot drill sidelock chuck for lathe

[Toolmaker51]

Not trying to highjack thehomeengineer's post, just donating some clarifying terminology.

For those on west side of Atlantic Ocean, in Britain and her many colonies 'slot drill' equal our end mill. Slot drill is a more descriptive name than end mill, certainly can drill; guided by a spindle. Drills do not have actual cutting edges on outside diameter, so they can be used in handheld equipment.
We call these tool-holder bushings. To us, collet signifies retention via gripping fingers, bushing is a cylindrical spacer or adapter body.
Shop or commercially made, the set screw is positioned over flat seen on end-mill shanks.
The location is quite standardized by diameter in keeping with design known as 'Weldon Shank' found in my numerous links...

Machine Tool Shanks (Tapers)