Hi Reefy - what thread pitch? If its course metric then an M8 is 1.25mm pitch. This gives a nominal pilot hole of 8-1.25= 6.75mm Also is your file set at 0.01mm ? If set at 0.1mm it maybe rounding up the pilot dia. Another tap chart says 6.7mm another says 6.8mm. All work if into steel go the big size if in aluminium go the small size. Peter
https://parts-badger.com/drill-tap-referencing/