The drills for ceramic restoration in the Z4 come in 3 sizes, in the top row, for conventional restorations. These drills are the G240, the G100 and the G060 which are respectively 2.4., 1.0, and 0.6 mm in diameter. The workhorse is the 240 drill that does the bulk reduction.
The rest of the the milling is done with the G100 drill. if you chose fine/detailed milling the G060 carves out the anatomy. The G120 T and G 060T drills are used for access channel milling for screw retained implant crowns.
Since the G240 does most of the work it also wears at a faster rate. A “tuned ear” can tell when the ceramic is worm and the drills is placing undue stress on the block material. If you let this go for too long, even before the software tell you there is enough usage left, either you will have the block break off the mandrel or you can break the bur (see attached video below and image of broken drill above)
Once you replace the 240 drill and the bulk reduction is done, the second drill does the rest of the work. For fine milling and more detail, you can select the G060 drill to finish the anatomy. or you can do it manually.