The SMART-BIT is a purpose designed pre-drilling and countersinking tool all in one. Some hardwood decking timber can be really hard and pre drilling the decking may be the only satisfactory way to install stainless steel decking screws. 

With SMART-BIT each countersink will be exactly the same depth, giving you a professional finish.
Pre-drilling and countersinking tool all in one
Smart-Bit works extremely well in all hardwoods and softwoods
Smart-Bit has a bearing-stop collar which eliminates countersinking too deep
Smart-Bit gives every countersink exactly the same depth, for a professional finish
 
TUFF Quick-Cut Countersink Tool
Includes 2x Pilot drills – 
1x TCT Pilot Drill for cement sheet board and compressed sheet, 
and 1x HSS Pilot Drill for hard or soft timber, plastic.
 
Designed for drilling and countersinking with one tool. 
For use in hard or soft timber decking, plastic, fibre cement board. 
Fully adjustable depth stop for accurate control of countersink. 
Rubber stop collar prevents tool from marketing the surface. 
Steel Bearings to ensure smooth operation.