It is quite easy to see that Or-Opt’s are a subset of 3-Opt’s as we exchange three special arcs with three others. The size of the neighbourhood is although reduced from O(n3) to O(n2).
Generally the size of a r-Opt neighbourhood is O(nr). The 2-Opt* is exchanging one segment of one route with a segment of another route. These neighbourhood-operators are sometimes
denoted crossover or simply cross.