Small diameter rotary drill bits using rolling disc cutters. Novel small diameter rotary drill bits with detachable pedestal mounted rolling disc cutters are provided. The bit body has a plurality of longitudinal edge mounting slots located at preselected angularly spaced apart locations. Preferably, the slots each have an upper protective ledge and downwardly extending sidewalls. A set of peripheral pedestal mounts each having a mounting portion sized and shaped to fit into a preselected mounting slot are provided and each is detachably mounted in its preselected mounting slot. In one embodiment, the longitudinally extending slots further comprise a wedge shaped edge portion, and the pedestal mounts have a complimentary angularly shaped portion, so that when the pedestal mount is brought into a close fitting relationship with the longitudinal slot, the pedestal mount and the longitudinal slot are tightly and securely interfitting. The pedestal mounts each include, at the lower reaches thereof, at least one small diameter single cutting edge rolling disc cutter. The rolling disc cutters are affixed at individually preselected radially spaced apart locations with respect to a central longitudinal axis forming the center of rotation of the rotary drill bit. Also, each of the rolling disc cutters is mounted at a preselected angle delta with respect to the central longitudinal axis forming the center of rotation of the rotary drill bit. Also, the rolling disc cutters are preferably detachably affixed to the pedestal mounts.