The seven sizes in the set range from 5/64" to just over 3/16" (2mm to 5mm), which will handle the pre-drill for screw sizes #2 to #9. They are particularly useful for short screws or screws in awkward places, both of which present problems for power pre-drilling.
In tempered steel, ferro-blacked in the traditional manner, this set was made specifically for us by a small European maker.