The Counter-sink drill bit has been specially designed for high minus lenses with deep back curves. 

When faced with high minus rimless frames, the nut used to secure the frame cannot sit flush against the lens.  As a result, the frame is flimsy and it is not possible to tighten the nut any more without chipping or cracking the lens. 

The specially designed counter-sink drill bit allows you to eliminate this issue by cutting a flat platform for the nut to sit flush and firm against the lens, thus providing a solid grip that is stronger and will result in a more secure hold. 



COUNTERSINK12 1.2mm

COUNTERSINK14 1.4mm