Custom Neodymium Magnets with Through Hole & Tap or Thread Hole

Question on Custom Magnet Manufacturing:
We're looking at some custom neodymium magnets concepts and have a few questions to ask.
There are 2 sample magnets (for reference only) - our new concept will have outside diameter & length slightly different than shown. Both below have .250" Dia. thru holes, and I like to know what is the smallest through hole you can make while holding similar tolerances so we can use on our new magnet concept.

NdFeB Permanent Magnet Manufacturer China Rare Earth Magnet Limited:
According to the outer diameter and axial height of magnets in the two drawings,
The smallest through hole achievable is 5 millimeter, while holding the same or similar tolerances.

Question about Tap Hole on Neodymium Magnet:
Further to our last enquiry, I have another few custom magnet manufacturing questions I hope you can help me answer.
Can metric tap holes (threads inside holes) size M2.5 x 0.45 Pitch x (minimum 5mm tap (threaded) hole depth) be made on both ends of the magnet instead of the 2mm or 1/16" Dia. dowels shown on the below 2 reference drawings? Because the tap hole depth is 5mm, how deep will you have to drill for the tap to achieve the required 5mm tap hole depth.
I understand either a "cutting tap" or "forming tap" may cut threads into the magnet material.
If tap holes cannot be made, can you let me reasoning behind this as I'm curious to know?

China Rare Earth Magnet Limited Couldn’t Directly Make Thread Hole on Neodymium Permanent Magnet:
No, threaded holes can not be made inside magnets, because magnets are very brittle themselves.
They will be cracked if we make threaded holes inside.
Conventionally we place a steel sleeve (with threads) inside the tap hole to achieve a threaded hole in a magnet.
But the tap hole in your design is just too small for this solution.