Metallics HSSC27E Drill Bit HD Cobalt St 135d SplPt 31/64" 5-7/8" YLW (1pc)

Cobalt is the reason to pick the HSSC27E over a plain high speed steel bit. The cobalt alloy holds its edge at the higher temperatures you generate in stainless, hardened steel, and heavy structural steel, where a standard HSS bit dulls or burns. Run it slower with steady pressure and cutting fluid.

At 0.4844 inch the hole is slightly undersize for a 1/2 inch bolt, so it is not a free clearance hole. It is the right call where you want a tight, close fit on a half inch fastener or anchor, or where you plan to tap or ream after drilling. For a loose clearance hole on 1/2 inch hardware, step up to 17/32 or 9/16.

A 135 degree split point self centers, so the bit bites where you put it instead of walking across the surface. On flat steel, strut, or an enclosure wall you can often skip the center punch and the pilot hole. The split also breaks the chip and clears it out of the flute, which matters on a hole this close to a half inch.

One bit per pouch. Order the quantity you need by the piece; it is not a graduated index set, so if you want a range of sizes you are buying each diameter separately.

The 5-7/8 inch figure is overall length including the shank, not flute length, so usable depth of cut is less than that. It handles normal electrical work, drilling strut, enclosures, plate, and beam flanges. For deep through holes in built up steel or for reaching into a stud bay, you need an aircraft extension length bit rather than this jobber length one.

Metallics part number HSSC27E. That covers the yellow finish cobalt bit at 31/64 inch diameter, 5-7/8 inch length, straight shank, 135 degree split point, one per pouch.