Originally Posted by Sherlock
The 25 would work good because the tail end is 20mm, which is a perfect 80%.
20mm minus the wall thickness. Think about it. A 80% FSA with one of my 25/12 fans would yield a diameter of 18.76mm. Area of I.D. minus Area of hub equals FSA.
With the 25/OT you would need a diameter of 18.53mm. Just shoot for 19mm.