A cutting tool holder adapted for mounting thereon a cutting insert having a top face, a bottom face and formed with an insert bore having an inner surface extending between the top and the bottom face. The holder comprises a seat defined by a bottom surface and at least one side wall angled to the bottom surface, a seat bore with a bore axis having an open end at the bottom surface of the seat, and a securing mechanism for securing the cutting insert in the seat. The securing mechanism comprises a securing pin received within the seat bore and having a body with an outer surface extending between a proximal end and a distal end of the body and defining a pin axis therealong. The securing mechanism further comprises a displacement arrangement adapted for axially displacing the securing pin along the bore axis of the seat bore between at least a first, mounting position in which the distal end protrudes from within the seat bore through the bottom surface into the seat to a first extent so as to allow the cutting insert to be placed within the seat, having its bottom face aligned against the bottom surface, and a second, securing position in which the distal end protrudes from within the seat bore through the bottom surface into the seat to a second extent, greater than the first extent, so as to engage the inner surface of the insert bore, thereby securing the insert in place.