Well here’s a possible reason to put the bolts in the Z stub parts…
No idea how it got like that or how long it’s been that way. Sat pretty well like that considering it’s totally wrong! (P.S. yes I know I need to get the airline out and get the crud off the rails before I ruin them 
)
I’ve put the bolt in just tight enough that it won’t fall out, it shouldn’t be providing any clamping force.