Drill bit and system for drilling a borehole

A drill bit for drilling a borehole in an object, having a central longitudinal axis and comprising:

• a pilot section with a cutting diameter Dp for drilling a pilot bore section of the borehole in the object;
• an under-reaming section with a cutting diameter Du in a following position with respect to the pilot section, the cutting diameter Du of the under-reaming section being larger than the cutting diameter Dp of the pilot section;
• a connecting shaft extending between the pilot section and the under-reaming section;
• a stabilising section located between the pilot section and the under-reaming section, wherein the stabilising section fits inside the pilot bore section and laterally stabilizes the drill bit relative to the object while allowing rotation of at least the pilot section relative to the object,
• wherein the stabilising section and the pilot section are substantially concentrally arranged;
• and
• wherein the pilot section is rotatable about the central longitudinal axis relative to the stabilising section;
• further including a locking means for selectively disabling rotation of the pilot section about the central longitudinal axis relative to the stabilising section.