Metallics HSSC17E Drill Bit HD Cobalt St 135d SplPt 21/64" 4-5/8" YLW (1pc)

The HSSC17E is a 21/64 inch diameter bit, with an overall length of 4-5/8 inches. The 21/64 size is the standard tap drill for a 3/8-16 thread, so it's the bit electricians reach for when they're tapping strut, channel, or steel for 3/8 inch hardware.

Cobalt is the point of this bit. The HSSC17E is a heavy duty cobalt drill, and cobalt alloy holds its edge at the higher temperatures you hit in stainless, cast iron, and tougher alloy steel, where a plain HSS bit work-hardens the hole and burns up. Run it slower with steady pressure and cutting fluid in stainless.

It starts the hole without a center punch. A 135 degree split point is flatter than a standard 118 degree tip and the split grind cuts at the center instead of pushing, so the bit bites immediately on flat steel rather than walking across the surface. On overhead work in strut or panel steel that is the difference between one hole and three scratches.

It's a straight shank bit, so it chucks into any standard three jaw keyed or keyless drill chuck. It is not a hex or SDS shank, so it will not lock into an impact driver's quick-change collet or a rotary hammer.

No. The HSSC17E is a cobalt twist drill for metal. Concrete, block, and brick need a carbide-tipped masonry bit, usually SDS or SDS-Plus in a rotary hammer. Using this bit in masonry will round the cutting edges off on the first hole.

The 21/64 inch cobalt bit is Metallics part number HSSC17E. Metallics numbers each fractional size separately in this cobalt series, so give the exact MPN rather than a size description when you're placing a repeat order.

One bit per order, supplied in a pouch. If you're standardizing a crew or stocking an MRO cage, order the quantity you need rather than expecting an assortment of sizes.