The K,B,C,D, and I in the tip of the soldering iron represent the mouth shape of the 5 basic grun electronic soldering iron tips. Grun electronic soldering iron head according to the shape of the head can be divided into these 5 kinds. K stands for K-tip, or knife shape. B stands for B, round. C means C, oblique cylindrical shape, also known as horseshoe type. D means D, flat shape. I means I tsui, also known as sharp head.