The potential of the triceps for growth is defined by the distance between the inner part of the elbow and the horseshoe.

Size                   Length of the triceps         Potential
7.62 см                Long                                 big
7.62 – 10.16         More than average            good 
10.16 – 15.24       Average                           average
15.24 – 17.78       Less than average              weak
17.78     and more     Short                           small

Despite all, you can have a massive triceps if its middle part is longer and massive. For this reason the table about the triceps is not as precise as the one about the biceps. I offer that these tables are used only for reference, not as definitive norms.
What are your chances to create big arms? As you can guess, not very big. In the best of cases they are one in a million. If, by chance, you are of the chosen ones and possess the genetic potential, it means you already have big arms without any special training. Then you think you have grasped the essence of bodybuilding and consider this site unnecessary for you.
If you are still reading, then you are probably of the opinion that your genetic potential is not enough, or am I mistaken? In fact, most of us possess the average or about the average potential. Others have a considerably better than average potential, so their results will be above the average.
What can become of you after all?
How big can your arms become, if you reach the highest of your genetic potential? In other words, what can your real achievements be? Are these the questions that torment you?
REAL OBJECTIVES
Set yourself real objectives; measure your arms. If they are 38 cm long, aim at making them 40; if they are 40 – then aim at making them 42. Move forward gradually. Don’t strive for quick final results. Step by step, slowly, but resolutely and constantly – this is the key to success. Leave all hope that in 6 weeks your hands will be like Casey Viator’s or Sergio Oliva’s. But you can be sure they will become bigger and better in relief and form. This will be the result of hard workouts, precise performing of the exercises, enough training, recovery and nutrition.
Be realistic in your expectations and the results will not be long.