Left Hand Twist Black & Gold high speed steel is the long lasting material when it comes to common drill bit materials, not only will the bit's structural integrity withstand tremendous heat and wear, but more importantly black & gold bits can drill through tougher materials than common HSS bits. With a Left Hand Twist 135 degree split-point, these drill bits will catch on the work-surface with greater ease and not wander all over the surface making scratch-marks. This means that after securing the bit in the machine all that is needed is a steady hand to point and apply pressure, and that's it. The Left Hand Twist straight round shank of our bits means you can use this drill bit with nearly all types of machines. The jobber length is the most commonly used length to diameter standard of drill bit in the US, the length is scaled according to the diameter of the drill head to give maximum force with maximum support so as to keep the bit from bending under the pressure, all the while keeping the machine a comfortable distance from the surface so as not to come in contact and scratch it. Included in the package is 20 pieces. Making for a total of 20 drill bits in total all with a length of 2-1/2".