If you have an older truck you will need metric bolts and fan as well. The revised fan parts are all metric.

The new bolts are metric M6x1.0, old are 5/16-18. Ford PN -N602527-S439 is what you should get, a pack of 4 bolts with lock washers attached. You will also need fan blade YA-259, 7C3Z-8600-C which has smaller holes for metric bolts mounting. Otherwise the new bolts could go through the holes of the old fan and most likely won't be mounted centered.

Ford Parts -N602527-S439 4 Pack of Bolts
Ford Motorcraft YA-259 or Ford Part 7C3Z-8600-C