Do you have any of your original fasteners? Going for concours specs?
Most were Lobo bolts on mine, but while some Giulietta nuts were unique in size, nuts are nuts. Most are hidden inside the bumpers where they are never seen. The overriders just get lock washers and nuts. Their threaded bolts are built in. The rear bumpers are kind of a balancing act to get all of the pieces straight and the overriders to sit right. If your brackets are nice and straight, have never been hit, you should be okay. If I remember correctly the threads are 1.50 pitch. Very little room between the rear chassis paint to tighten anything once in, so try to first get it true on the bench or floor. the original side bolts for the bumper ends had a pointed end and a specific length. Get a friend to help...or your fresh paint will likely suffer.
I found the front bumpers’ sweet spots are dictated by where the overrider brackets attach to their built-in threaded nuts on the body, so much more simple. Again, mostly hidden, any Lobo markings unable to be seen, with the exception of those overrider brackets.
Alfa didn’t use stainless bolts and nuts on these cars, but should have. If hidden away, I did use SS on some of those. Belmetrics or McMaster-Carr (or any good hardware) has the right size metric bolts, washers & nuts. They also have black zinc fasteners for the ones that were originally black oxide.
A lot of the fastener sizes are not in the parts books. Carl750 may be more likely to have that info, thankfully.
I prepared small ziplock bags of M4,5,6,8,10, etc of bolts and nuts as guides to determine the correct pitch and length of their use as I went along. Guessing pitches is not always an exact science.
There always seemed to be one missing from my original lot for each installation. But, sometimes the same amount of certain size bolts and nuts helped me to determine where they went however. Empty canned cat food case boxes can be your friend for sorting them out and spotting what you need.
Getting them all sorted for the correct cad finish plating or black oxide (or the longer lasting black zinc) is like working a tedious puzzle. Good luck.
