Drilling bit and holder for drilling bit

A drilling tool, comprising:

• a holder having a longitudinal axis and a forward end having a clamping slot;
• a drilling blade secured in said clamping slot;
• the drilling blade having a rear end, a forward end, opposite first and second side faces, and opposite end faces, and being of generally rectangular cross section, the blade having a base portion for engagement in said slot at said rear end and a cutting portion projecting out of the slot up to said forward end;
• the cutting portion having first and second, diametrically opposed cutting edges and first and second, diametrically opposed parallel contact surfaces on said opposite side faces at the forward end of said blade, the spacing between said parallel contact surfaces defining a first thickness;
• the blade having an increased thickness greater than said first thickness in the region of the cutting edges;
• and
• the blade having an arcuate recess in each side face extending up to the respective cutting edge.