It is an M8 metric size on the port going into the spindle, and a 1/4" compression on the other side.
Is the M8 port a M8x1.25 or M8x1?
If you are referring to the book build, use a chamfer bit that is large enough to create a chamfer for most of the edge of the 3/4" thickness of the board, but still has a sliver of space for the bearing on which to ride.
Mine is M8x1mm. I replaced the stock fitting with a brass hose barb and used "steel wire reinforced vacuum hose" with a 1/4" ID because it resists kinking and collapsing.
Click the link to respond:
on the 2.2Kw water cooled spindle, what is the cooling port thread type and size?