Wall thickness, which in turn affects the inside diameter, the water-carrying capacity and the rated internal working pressure. Type L, the next heaviest, has an inside diameter of 0.545 in. and a wall thickness of 0.40 in. Type K, the heaviest of the three, has an inside diameter of 0.527 in. and a wall thickness of 0.049 in. Although these increments may seem like small differences, they change the physical characteristics of the tubing considerably. This difference doesn't amount to a hill of beans, though, for residential plumbing because working pressures are so low.
Copper tubing is available in both hard and soft tempers.
Hard copper, what the industry may call drawn tubing, is sold in straight lengths of up to 20 ft. Soft, or annealed, copper is sold in rolls up to 100 ft. A bending temper tubing also is available in straight lengths. One advantage of using rolled copper is that a long run won't require as many soldered connections. There, according to the code, type L must be used.