Once the cross holes are drilled the next step is to drill out holes to be
tapped for set screws that hold the jet nipple in place. These two holes
are drilled in the lip of the large end of the reducer bell. Make sure to
center the holes (punching helps). I used #6-32 hex-key set screws. Use a
#36 drill for this size hole. I then deburred and made a slight
countersink using a #24 drill bit as shown here.
Step 5: Tap
the holes for the set screws. I quickly realized that I did not have a tap
handle with a small enough collar to hold the #6 tap. Crescent-wrench to
the rescue. Fortunately this set still has fairly tight jaws so there was
no slop to cause slipping on the end of the tap. Plenty of machine oil and
working the tap both forwards and backwards make this part easy. Slow and
steady is the key to not breaking the tap.