The loop to loop

Tie a double over hand loop into both lines to be joined.

Pass one loop through the other.

Thread the end of the shorter line or the hook end of the hook length through the inner loop.

Pull this line all the way through feeding the double over hand loop through as well. So that the knot appears as that below and pull tight. To untie this knot hold both ends of the knot and push them together and unthread the hook length.