First of all, thanks to all who have posted on this forum - I purchased a suburban this past summer and have used the info here for numerous projects/maintenance. My suburban - 1999 K1500 with the 350 Todays project was replacing the water pump. I usually try to search this forum and read through the manual prior to starting. The biggest challenge for replacing the water pump seems to be the fan clutch nut. After unsuccessfully trying three sets of tools from Autozone and having multiple employees state the nut is reverse thread, here's what I found: (I apologize if this is has been posted before and I didn't see it) The nut on my '99 is NOT reverse thread - it is threaded like any other normal nut/bolt (I found this out after using multiple tools, a cheater bar, and a big hammer - after getting nowhere I tried the other direction for giggles and wouldn't you know, it loosened right up So the nut does not get tight in the same direction as the fan blades spin - which I guess is not the normal. Napa had the correct tool for the job - its new part # is 41570 (the "loan-a-tool" one I got was part #62331, but has been changed to the above #) The fan clutch nut size is 36mm - the Napa tool has the correct wrench - I've read online where others have used an adjustable wrench with a pipe cheater and a hammer, but the Napa tool is works really slick (and free). The rest of the job is a piece of cake. Hope this helps and saves some time.