HSS Straight Shank Twist Drill (4.0mmx2pcs)

Stainless steel work hardens. That means the metal becomes harder when it is deformed, and drilling deforms it. Cut it properly and the hardened layer comes away in the chip. Fail to cut it, and the hardening stays in the workpiece, right where you are trying to drill, and it gets harder with every second you spend rubbing at it.

That single property causes almost every ruined bit and every hole that would not start. The classic sequence goes like this. Someone starts with a fast drill speed and light pressure. The bit skids and polishes rather than biting. The surface hardens under it. Now the bit genuinely cannot cut, so they press harder and go faster, which produces heat, which takes the temper out of the bit, and within a minute both the bit and the spot on the workpiece are finished.

The method that works is the opposite of instinct at every step. Slow speed. Heavy, constant feed pressure, enough that the bit is always cutting. Never let it spin without advancing, not even for a moment. Cutting fluid. And do not lift and re enter a hole repeatedly, because each restart is another chance to glaze the surface.

Cobalt steel makes this easier by holding its edge as the temperature rises, but it does not repeal the rule. The technique still matters more than the bit.

Four millimetres suits small fixings and pilot holes in stainless sheet, tube and section, fabrication and bracketry, and marine, food and process equipment.

The spec's references to carbide and to percussion drilling belong to a masonry bit and have been disregarded; this is an M35 cobalt high speed steel twist drill.

Buyers are stainless and general fabricators, marine and food equipment trades, engineering shops and maintenance fitters.

Ask on 94 77 111 8880 about cutting fluid with the bits. We deliver island-wide.