The nut size is 24mm but I don't know the thread spacing. Many members have needed to get them from another Fiero since they apparently are rare.
Edit to add....here are the replacement part numbers:
SPINDLE-TITE-05189
HELP-04989.....as in the "Help" section of your local parts store.
Here is the website that sells them. They say it is a 30mm nut for the rear but do not specify the front size. The top one is the front and the lower is the rear nut.
http://www.rockauto.com/cat...2BNut%2BKit%2BDORMAN[This message has been edited by IMSA GT (edited 09-15-2010).]