N606689-S2

This an M8-1.25mm screw with a captive washer and it is 28mm (1 1/8") long.  However, I can't find a source for this screw, so if you need one I think a shorter screw would work fine.  I say that because the threads of the screws stick through the nuts by 1/4" even on the lower bolt, so a 1" long screw like the N807524 should work fine.