Re-use all the old nuts, washers, plastic insulators, O'rings and bolts.
It is very important you replace the parts in the order they was removed. The small electrical connection coming from inside the solenoid MUST go between the copper bolt and the copper contact (SEE PHOTO)
When the nuts are finally tightened it may lift the edge of the contact, this is not good. Both copper contacts MUST be flat and level or contact life will be greatly reduced.