cheers guys 8.8 grade is just a little better than 316 stainless but there is a significant cost saving even if you factor in plating it. However i think it would be a lot nicer having stainless and its readily availble for me (can get it from scrap basically, could even make it from 17-4 or duplex (uns31083 i think)if i fancy
) only thing to note is that general a2 (304 stainless) would be useless in this aplication.
I would have thourght that you would have been able to turn the bungs with a little effort. You need to have the force through the bolt and the delrin would deform under that load. So you would have the spacer machined slightly longer 0.001" so that you got the correct torque on the bolt.