Product Review

This Dormer A191 jobber length drill bit set contains 13 high-speed steel drill bits, including metric sizes 1.5 through 6.5 mm in 0.5 mm increments and sizes 3.3 and 4.2 mm, with a black oxide finish and a 118-degree conventional point for use in general-purpose applications on ferrous material. High-speed steel (HSS) provides hardness for wear resistance, and the black oxide finish acts as a lubricant to reduce wear while promoting chip and coolant flow. These jobber length drill bits have a drilling depth up to four times their diameter. The round shank accommodates most drill chucks. The set comes in a plastic index case with labeled compartments for identification and organization. Drill bits conform to Deutsches Institut für Normung (DIN) 338 standard. Drill bits are cutting tools used to make holes in a range of materials using machines such as handheld portable drills, machining centers, and lathes. Drill bits come in a variety of lengths and types, the most common of which is the twist drill bit. The round, twisted shaft of the twist drill bit typically has two cutting edges and flutes. The helical twist of the flutes brings chips up and away from the cutting edges and allows for coolant to reach the cutting edges. Jobber length twist drill bits, the most common length of twist drill bit, offer a good compromise of length and reach to work with the widest range of materials and applications. Mechanic's length twist drill bits (also called maintenance length) are a little shorter than jobber length and less prone to deflection when drilling. Short length twist drill bits (also called stub or screw-machine length) are the shortest and stiffest twist drill bits, helping to reduce the chance of deflection or breakage when drilling. Reduced shank drill bits (also called Silver and Deming drill bits) have a shank that is smaller in diameter than its shaft, permitting drilling machines with either a 1/2" or 3/4" drill chuck to create large holes. Long length twist drill bits (also called taper length) are a little longer than jobber length, allowing for deeper holes and longer reach. Extra long twist drill bits (also called extension) are longer than long length twist drill bits for greater reach or for drilling deeper holes.Dormer Pramet manufactures solid cutting tools under the brands Precision Twist, Dormer, and Union Butterfield.