T45 89mm Dome Spheric Button Threaded Drill Bit for Rock Drilling The T45 89mm dome spheric button drill bit is a threaded rock drilling bit designed for demanding drilling applications in mining, quarrying, construction, tunnelling and rock excavation. With an 89mm diameter, T45 threaded connection, dome/spheric button configuration and normal body design, this drill bit provides a balanced cutting structure for efficient rock penetration and reliable drilling performance.