What holes were open with when you were putting the fuel rail back on (or was it coming off) on a 96up blazer? The nut is metal so magnetic but its small and light. Are you sure the nut is not sitting along the valve cover and lower intake in that channel between them??? I always tape over the openings in the intake (if dist out) as I do the fuel rail with those nuts and 4 o-rings and 4 flat washers in the spider. I have dropped them too but look around with a strong light at several angles and good chance that nut is out there.