Howdy NH, square bottoms on the iron? Putting a tenon on iron isn't as east as it looks.
Thanks Chris.
How about square holes? and chisel the top line first in place. Why drill first? I would just make a good guess as to where plumb is after a little flat to guide me.
Big fan of square holes, makes it harder to twist.
I totally agree with you in regards to the square holes (to resist twist, easy to chop by hand, etc), however it would seem he wanted a jig to do round holes for a cast iron component, so I assumed the 'tenon' on the casting was round as well. Need some clarification on that i guess.