Use of Self Tapping Screws can save considerable time and trauma. Pull out strength is not affected provided the self tapping flutes lie outside of the cortex.Self Tapping Screws are less effective in dense cortical bone. e.g. calcaneus. It is advised that an appropriate tap be available should the need arise. Drill data: Pilot Drill 1.1mm, Clearance Drill 1.5mm.