Propshaft question

[AM400]

Just replacing the bolts on the prop as part of a bigger job. On the prop there is a threaded collar at the gearbox end. This was very loose on mine so naturally I started to tighten it up by hand. Question is should this be done up really tight or hand tight? Not being really sure what purpose this serves I dont want to give it too much.

Can anyone enlighten me?

Andy