What is the basic difference between Pipe specification A106 Gr.A / Gr.B/ Gr.C.? Answer: Difference is due to the Carbon content.% of carbon content in : I. ASTM A106 Gr. A – 0.25 % II. ASTM A106 Gr. B – 0.30 % II ASTM A106 Gr. C – 0.35 %.