"John Hofstad-Parkhill" wrote in message
news
jt:

I'm pretty sure the flat on the shank of the mill is for the set screw -
as
in an end mill holder. The flat would resolve any issues that would come
up
with scoring the shank.

After years of following this newsgroup, it seems that an end mill holder
has an edge over a collet for milling. I just made some 3/8" end mill
holders for my CNC mill using 23/64" drill & 3/8" reamer.

Should I use an exact 3/8 reamer, or one that's oversize?