Improperly rolled joints create additional expense to correct,whether they are under-rolled and can be corrected merely by rerolling, or over-rolled and require removal and replacement. The optimal joint is one that develops a leak tight joint with adequate strength for the service intended with the minimum amount of cold working or reduction of the tube wall. Experience indicates that joints of this type are obtainable with non-ferrous tubes in surface condensers by expanding to a wall reduction of 3% to 4% after metal to metal contact of the tube O.D. with the tube sheet hole. Steel tubes in heat exchangers may require wall reductions of 5% to 10%; soft copper and aluminum tubes in heat exchangers also require larger wall reductions in the area of 8% to 12%. Boiler tubes requiring development of optimum joint strength require wall reductions of 12% to 14%.