a tool used in manufacturing circuit board holders from sheets of material has a working face for forming embossments on the sheets by repetitively striking the sheets therewith . the working face includes an h - shaped formation for forming two separate halves of an embossment on the sheet of material with one strike , of which , of the two separate halves , one is delimited by the upper parallel lines of the h and the other is delimited by the lower parallel lines of the h . in a method using such tool , the sheet of material is struck once with the tool , the working face of the tool is moved relative to the sheet in a direction of the parallel lines of the h by a predetermined distance , and the sheet material is again struck with the working face of the tool so that an embossment is formed on the sheet which is delimited by a pattern left on the sheet of material by the parallel lines of the h pointing in one direction at the first strike and by a pattern left on the sheet of material by the parallel lines of the h pointing in the other direction at the second strike .