R32 89mm Dome Reaming Button Bit - Threaded Rock Drill Bit The R32 89mm Dome Reaming Button Bit is designed for controlled hole enlargement after a pilot hole has been drilled. It is commonly used with a compatible pilot drilling system to enlarge the existing borehole to the required diameter. The bit features an R32 threaded connection and an 89mm (3-1/2 inch) reaming diameter . Its dome-shaped carbide button configuration is designed for stable contact with the rock