There are two screws used, 359121-S42, 5/16-24X3/4 hex, 13/16 flange washer, and 378180-S2, 5/16-18X3/4 hex, 13/16 flange washer (I use the term flange washer to describe the permanent washer as apposed to a separate disc washer). From Osborn, the 5/16-24 screw was referenced in the Chassis section for 64 and 65, the 5/16-18 screw is referenced in the 65 Body section. The 5/16-18 appears to be more common. No plant or change over is known (yet).
Pictures 1, 4 and 5 only show the tip of the 5/16 screw, the prominent feature is the fan shroud screw.
Picture 2 shows the hex head of either 359121-S42 or 378180-S2, as above.
Picture 3 shows a tip.
Picture 6 appears to show a different head.
Jim