Connecting Cable Into the Switchgear

Considering the OP refers to nuts and bolts, I think bigger than your trying to sell.

your bolt should match with the hole. Your nut should suitable for bolt.(otherwise it will lead to divorce) This is applicable for everything.....Thank god that you are electrical engr only...i can not imagine if you were a doctor!!!!

Put really simply that depends on the size of the cable, bus bar, cable lug and overall current rating. Additionally it also depends on environmental and mechanical forces and whether or not the metals are dissimilar (eg- copper to aluminium joint). The list goes on....

So in short, there is actually a lot going on in an electrical joint. There is plenty of general information on the internet and also previous CR4 threads discussing particular elements of current carrying and bus bar joints.

For a really quick guide (if you are not mechanically minded) check out the commercially-available cable lugs that match the cable that is suitable for your current, that will give you a starting idea of what size bolt to use. As a really, really rough overall guide M8-M16 size stainless steel 304 or 316 bolts with corresponding stainless steel 316 or 304 nuts, washers and spring washers is a good place to start, but is not suitable for all applications.