Drilling with mixed tooth types

1. A rotary-cutter rock-penetrating drill bit, comprising:

a plurality of rotatable elements, each bearing thereon first and second pluralities of inserted cutting elements which incrementally remove rock as the drill bit is rotated and advanced;

wherein at least some of said first and second cutting elements remove rock from a shared location;

wherein said first and second inserted cutting elements have different diameters, and

wherein at least one single non-gage row of inserts on at least one rotatable element includes ones of said first and ones of said second cutting elements.

2. The bit of claim 1 , where said rotatable elements are attached through a rotary joint to arms which are affixed to a body having an API thread.

3. The bit of claim 1 , comprising only three of said rotatable elements.

4. A method for rotary drilling, comprising the actions of:

(a). applying torque and axial force to a bit according to claim 1 , while

(b). pumping drilling fluid through a drill string to which said bit is connected.

5. A rotary drilling system, comprising:

a bit according to claim 1 ,

a drill string which is connected to conduct drilling fluid to said bit from a surface location; and

a rotary drive which rotates at least part of said drill string together with said bit.

6. A cutter for a roller-cone-type rock-penetrating drill bit, comprising:

a tapered cutter body bearing a gage row, and at least one other non-gage row of cutting elements;

wherein said other row includes a single row of first and second different types of said cutting elements, wherein said first type has a larger diameter than said second type.

7. The cutter of claim 6 , wherein said body is steel, and said cutting elements are cermet inserts.