As topictitle says.

I can imagine that headstuds hold the head in place, but main studs?

main studs hold the caps which hold the crank. stock arent studs i think there bolts and are only good up until a certin psi. studs are a stud and nut which replace a bold and can withstand more psi. :biggthump

head studs do the same except that they hold the head :biggthump

Thanks!