Stupid Fuel Sender Question

I realize to a seasoned pro this is going to sound about as dumb as $h1t but here goes. The rubber gasket for the sending unit to the tank does it go on the tank side or the locking ring side. I want to say tank side but it is currently on the new sender that is in the box lodged with the lock ring.
It goes between the tank and the sender,then clamps down with the locking ring.It,s always better to ask first before having to do it twice.Good luck.