GTN 750Xi rack mount screws

[turbosuper]

The Garmin GTN 750Xi installation manual shows to use 6-32 flat head screws to mount the rack. Using MS24693-S26 100 degree recessed head screws, the screw head bottoms out without being tight on the rack. The rails are 6.30 inches apart. A countersunk tinnerman washer needs to be used to get the screws to be tight on the rack. Should different screws be used?

 

[TiltOn22]

You could rivet the racks in place if you'd prefer