Here's the Papst, about .24 inches. I couldn't get my caliper to fit in the case very well, but the case tabs are about .22 inches. I had to bend them to make the fan go in and then push hard. Once it did, it is really solidly locked in.
This may be because I did not read directions :-). Apple supplied a "Correction for page 17" which instructs the user to rotate the fan by 90 deg compared with the original page 17. I had forgotten about the correction and installed the fan per the originals. This might be the cause of the problem