It's just what you'd think, L-shaped, actually one right- and one
left-handed. The books I have recommend locking the clapper block in
use. Slot the center first, then work out the sides with the tools.
The older books showed how to forge the tools. Sounded like a lot of
work, so I found other ways to fabricate T-slots. If you're just
cleaning up cored castings, that's different.

Stan