There are a bunch of threads on here asking for the sizes of the OEM plenum nuts & bolts. There's some info in the FSM, but, surprisingly, even Nissan's fast system doesn't have the complete specs. Anyway, the OEM sizes are below - add 8-10mm if you're running a 5/16" plenum spacer.

Intake Manifold Collector (Upper)



Bolts 1, 3, 6, & 9 = M6 x 1 x 60mm (red)
Bolts 2, 4, & 5 = M6 x 1 x 45mm (yellow)
Bolts 7, 8, 10, 11, 13 - 16, & 18 = M6 x 1 x 25mm (green)
Nuts 12 & 17 = M6 (green; these nuts & studs are sometimes replaced with M6 x 1 x 25mm bolts in aftermarket applications)


Intake Manifold Collector (Lower)



Bolts 1-6 = M6 x 1 x 70mm (blue)
Nuts 7 & 8 = M6 (violet)

hopefully this helps someone who wants to go back to stock, but has misplaced their OEM bolts.

 

Well this thread is awesome. My brother broke one of my bolts that are supposed to be torqued in Inch-Pounds (The blue bolts) and we needed to find replacements. Thanks!

 

I found them at Lowe's near me. They are pretty organized and have a drawer in the hardware section specifically for M6 bolts. I found all the sizes I needed in there.

 

glad it helped

 

Thanks google and OP