CONDOE_WON,
The bolt required for the BVM fans is a 1/4-28 NF (FINE THREAD, NOT 1/4-20 NC COARSE THREAD.). A 20 thread per inch bolt will not work in this application.
I may be blind, like I stated before, but I know a little something about threaded fasteners. Here's your lesson for today.

The number after the majordiameter is the thread count per inch. In effect, 20= 20 threads per inch, and 28= 28 threads per inch.
EXAMPLE: A 1/4-20 bolt or screw, or a nut for that matter, has a major diameter of 1/4", and 20 threads per inch.

Micro Fasteners still DOESN'T offer a 1/4-28 bolt.
Here's the pudding you mentioned, and the proof is inside.
Please...don't try jamming your newly purchased 1/4-20 bolt into your BVM fan.

Check it carefully, and you will find that I'm correct.

Harley Condra
BVM REP