When tapping, it's critical and you need to go forward and back to clear chips. 
The hole is 1-3/8.  After I threaded it, I cut the nut out. 
 I should have flattened it before drilling to ensure the hole was square to the nut.  A bit of sawing & planing got it close enough to use for the leg vise to replace the pipe clamp one I'm using here.
I should have flattened it before drilling to ensure the hole was square to the nut.  A bit of sawing & planing got it close enough to use for the leg vise to replace the pipe clamp one I'm using here.


 
