I'm messing with screws for fans myself. Doing some final truing up and measurement checks and realised (why after all these years) that I don't have sufficient clearance between tube and fan to use regular screws. But the XSPC radiator uses 6-32 UNC threads, and finding UNC bolts in metric lengths is impossible, especially when you're using a 15mm thick Noctua fan.
After digging through numerous places I'm now chopping down countersunk 3/4 inch bolts to 18mm length and drilling countersinks into my fan so it's all flush and doesn't interfere with the tube over the top.
So forgive me for being a little triggered by your fan screws