A twist drill is usually the first cutting tool a workshop buys, and for good reason: one HSS drill can follow a pilot hole, open it up, cut through steel angle, brass, copper and most plastics without a second thought. The problem is not capability but choice. Between flute designs, point angles, coatings and shank styles, two seemingly identical drills can behave very differently in the same material. This guide walks through the decisions that actually matter when selecting HSS twist drill bits for production or resale.
What HSS Really Buys You
High Speed Steel is a family of tool steels that keep their hardness at the high temperatures generated by real cutting speeds. A standard M2 HSS drill will soften and lose its edge around 550 °C, while the material being cut is frequently above that temperature at the point of contact. The trick is that M2 resists softening long enough for the heat to conduct away through the drill body and into the workpiece and chips.
For most general workshop and production use, M2 is the right economic choice. When the job turns serious, HSS with added cobalt — often labelled HSS-Co or M35/M42 — holds its edge at higher temperatures and is the standard recommendation for stainless steel, heat-resistant alloys and any material that work-hardens. Cobalt drills cost more and are slightly more brittle, so they should be reserved for jobs that actually need them rather than used for everyday drilling in mild steel.
Flute Geometry: More Than Chip Clearance
The flutes of a twist drill do three jobs: they form the cutting edges, they curl the chip, and they carry the chip away from the cut. Straight, low-helix flutes are efficient in brass and thin sheet, where a conventional helix would grab and pull. A standard 30-degree helix is the workhorse geometry for general steel and most metals.
For deep holes, look for high-helix or parabolic flute designs. A parabolic flute is wider than a conventional flute of the same body diameter, which lets a long continuous chip curl without jamming. If a job needs a hole deeper than about three times the drill diameter in a stringy material such as aluminium or mild steel, a parabolic-flute drill is the difference between a clean bore and a drill that snaps from packed chips.
Point Angle and the Split Point
The point geometry controls how the drill starts, how it cuts, and how much thrust the operator or machine must apply. The conventional 118-degree point is the default for most materials and suits general steel, wood and plastics. The flatter 135-degree point is the better choice for harder materials and for stainless steel: it shortens the cutting edge per revolution, reduces the thrust needed, and resists work-hardening of the surface.
The more important upgrade is the split point. A standard chisel edge is a straight line across the centre of the point that does not cut — it pushes and rubs, which causes walking and high thrust. A split point (sometimes called a crankshaft or self-centring point) grinds that chisel into two smaller cutting edges that start cutting immediately at the centre. Split-point drills start on the mark without a centre punch, drill rounder holes and require noticeably less feed pressure. For any job that runs in a drill press or CNC spindle, a split point should be considered mandatory rather than optional.
Coatings: When They Pay for Themselves
Uncoated bright-finish HSS drills are the low-cost baseline and are perfectly adequate for short runs in mild steel and soft materials. The first step up is black oxide, a surface treatment that retains lubricant, resists light rusting and slightly reduces friction — a meaningful improvement for general production drilling at a modest premium.
Gold-coloured titanium nitride (TiN) coatings add real hardness and lubricity, extending tool life in abrasive conditions and reducing the tendency for chips to weld to the flutes in softer, gummy materials. For stainless steel and other work-hardening alloys, titanium aluminium nitride (TiAlN) or similar advanced coatings outperform TiN because they stay stable at higher cutting temperatures. As a buying rule: match the coating to the material and the run length, not to the colour. A coated drill that is reground loses its coating at the cutting edge and should be treated as an uncoated tool afterwards.
Shank Type and Machine Fitment
Twist drills for hand drills and drill presses use a plain cylindrical shank with a diameter tolerance to suit a three-jaw chuck. The two things to check are shank tolerance and length class. Jobber-length drills are the everyday standard; stub-length drills are shorter and therefore stiffer for starting accurate holes; reduced-shank drills carry a smaller shank than the cutting diameter, allowing a large bit to fit a 13 mm chuck — useful on site, but the reduced shank limits the torque that can be applied.
Straight-shank drills used in production machine tooling are held in collets or chucks, so the shank diameter tolerance matters far more than it does in a hand drill. If the drills are intended for CNC work, specify the shank tolerance class at order time rather than accepting whatever standard stock delivers.
Reading a Specification Label
A specification that says "HSS" tells you very little by itself. The label worth reading lists the steel grade (M2, M35, M42 or HSS-Co), the point geometry (118°/135°, split or not), the coating, and the applicable standards for diameter tolerance. When comparing drills from different suppliers, compare like for like on those four points, not on price alone. A cheap M2 bright drill with a conventional point will always cost less than a cobalt split-point drill, and it should — they are different tools for different jobs.
The Buying Shortlist
For a balanced workshop stock, a practical HSS programme covers three groups: general-purpose M2 bright or black-oxide jobber drills in the common metric and fractional sizes; a cobalt (HSS-Co) split-point range from 3 mm upward for stainless and alloy work; and a high-helix or parabolic range for deep and stringy materials. Add reduced-shank drills for large diameters and a stub-length set for accurate starting, and the coverage is complete for most metalworking shops.
FANXI manufactures the full HSS twist drill family: M2 and cobalt jobber drills, high-speed and parabolic-flute drills, reduced-shank and long series, together with HSS drill bit sets for retail and industrial programmes. Private label, custom point grinding and packaging options are available through our OEM programme, with samples supplied on request.