Seat belt and seat bolts????

[bearskinrug]

Hey guys anyone know what size bolts are used to secure the rear forward facing seat and seat belt in a 95 NAS d90?
I'm trying to use existing holes in my bed to secure loads/build a load floor. There are threaded nuts already beneath these bolt holes attached to the bed ready to accept a bolt I just can't figure out which size....
Thanks for any help!
Patrick