Interesting update on "crappy" repro fan shrouds

Thanks for the pic and info guys. Forgive me but, there's space or a cavity molded in below the mount that would allow room for a u-nut - but a lot more than necessary. What prevents you from crushing/cracking the shroud when you tighten the bolts down?

What size thread on the bolts/u-nuts? 1/4"-20?

shroud mount.jpg