In selecting bits from these kits I was able to find a few bits with sufficient precision to cut 0.1mm line on 2 oz FR4 PCB material with 0.15 line. Quality control is less desirable. Some bits are much wider, some are off-center, and a few have the ability to create 0.05mm lines, but I haven't tried them yet. When routing insulation in multiple passes, the right size is best. YMMV, but before you start cutting, look at each bit in the field microscope as the spindle spins. receive. But atβ¦