If you are thinking about purchasing COBALT tools, it is important to understand that the term "cobalt" refers only to the alloy steel employed in the manufacture of the cutter. For example, "cobalt jobber drill," refers to a jobber drill manufactured from cobalt alloy steel. Cutters of many types such as drills, countersinks, hole saws, reamers, taps, end mills, hacksaw blades, etc., are readily available as cobalt tools. High cobalt alloy tool steels are best known for having excellent wear and corrosion resistance over a wide variation of temperature ranges.
In addition, the cutting tool industry has adopted a uniform 135 degree split point for all cobalt drills from 1/16" and over. In wire gauge sizes, split points are available down to #52. Recently some manufacturers have started to produce drills with split points as large as 1-1/2" diameter.
There are two principal classes of cobalt cutters:
Those manufactured from M35 cobalt steel which is similar to M2 (standard high speed steel) but which contains 5% cobalt added. The addition of cobalt increases heat resistance, allowing the higher speeds needed to cut stainless and other hard materials.
M42 is a high speed steel alloy similar to M35, however it contains roughly 8% cobalt, enabling it to withstand even higher cutting speeds and temperatures, without losing temper. Additionally, wear and chipping are reduced particularly during interrupted cuts.
High speed cobalt tools are often identified by the letters HSS-Co, either stamped or electro-etched on the shank of the tool.
In recent years, drill manufacturers have adopted a uniform bronze color as an industry standard to identify cobalt tools. This color should not be confused with the bright gold color associated with TIN-coated cutters (see Tin Coated drills).
Cobalt jobber drills are the preferred option for experienced mechanics in many diverse fields such as lock-smithing, HVAC, automotive trades, machinery repair, etc. Because of their capacity to drill through tough materials, the need to change bits is minimized; and, because of the 135 degree split point, they work as well in the field as in the shop.