GMD rock tools for top hammer drilling are designed to transmit intensive impact energy into the rock with the least possible loss of energy. The result is good rock breakage, , high penetration rates and high productivity. This, together with optimal hole quality, great reliability and long service life, gives the best possible blasting results, outstanding drill-steel economy and low total cost.GMD offers a complete selection of Top Hammer Drilling Tools to meet all of your drilling needs,which are suitable for any type of drilling application in mining, tunneling, construction and quarry work.Specification of R28 Drill Bit, kindly check below:A comprehensive range of various button bits shown as below:Thread type: R28Head diameters: 33mm ~ 76mmFace designs; flat face,Carbide shape: Dome, Ballistic , Semi-Ballistic,Skirt designs: StandardApplication: Drifting and TunnelingR28 Drill Bits for Drifting and Tunneling Name Code No. Thread Diameter Gauge Front Skirt Design Weight Threaded Button BitsQ7-36-R28R28365*8mm2*7mmStandard0.42Q7-38-R28R28385*8mm2*8mmStandard0.48Q7-41-R28R28415*9mm2*9mmStandard0.56Q7-43-R28R28435*9.5mm2*8mmStandard0.68Q7-45-R28R28455*10mm2*9mmStandard0.72Q9-45-R28R28456*9mm3*8mmStandard0.72Q9-48-R28R28486*9mm3*9mmStandard0.89Q9-51-R28R28516*10mm3*9.5mmStandard0.97Notes:Special sizes may be available upon request.How to order?Button Bit: Diameter   + Thread + Skirt Shape + Face Design + Insert ConfigurationHow to Choose the Right Button ShapeButton Shape and ApplicationButton ShapeApplication Domed/Round ButtonDomed/Round buttons are suitable for very abrasive   and very hard formations.Parabolic /Semi-Ballistic ButtonParabolic buttons are usually used as gauge buttons and front buttons, suitable for medium abrasive and hard formations.Key Words:R28 Drill BitsR28 Threaded bit,thread button bit,R28 button bitR28 Button Bit for for Drifting and TunnelingThread Button Bit for for Drifting and TunnelingButton Bit for for Drifting and TunnelingButton Drill Bit for for Drifting and Tunneling