Most cooling fans are made to be cheap and thin and in most cases move less CFM than stock units. Also most fans measure there CFM out in the open with no resistance. SPAL fans out perform ! We have used them for 12 years and havn't seen any fail and they go into all our builds.
Here's some examples

Civic 1/2 size radiator 13" SPAL fan


S2000 shroud built by LHT with twin 12" SPAL puller fans



This way 100% of the radiator has air been drawn through it make it upto 40% more efficiant than 2 fans without a shroud.



The shroud is 1" thick and the fan at there thickest part 2.4".

We have many SPAL in stock