rear sub-frame nut/bolt size?
 

Can anybody help me out with this?

Bump

the Big nut that holds the subframe to the car?..it sits on a stud attached to the car?
That nut is 21mm.
The subframe gets installed on that Big "body pin"(hanging under the car) and then bracket goes on and holds the Subframe assembly along with that 21mm nut.The bracket is also held up by a 14mm nut on the Underside of the rocker panel.
That nut also attached to a small stud.

Are you wanting to know the hex head size or the thread pitch to get a replacement?

I tried to get thread pitch but must have missed it looking at the threads on Subframe.
BUT I did find this "Just in case"..
Link: https://www.rx7club.com/2nd-generati...ctures-518052/