Precision Twist Drill 5998191 Cobalt Jobber Drill 31/64 in

Product Description

The PRECISION TWIST DRILL 5998191 is a cobalt jobber-length drill bit designed for heavy-duty drilling in steel and other demanding workpiece materials. Ground to a 135-degree split point with web thinning, it self-centers on entry and reduces the thrust force needed to start a hole, making it suitable for production and maintenance drilling alike. The straw oxide finish provides moderate lubrication and corrosion resistance during cutting. At 5.875 inches overall length with a 4.375-inch flute length, the 5998191 fits standard drill chucks without modification and handles through-hole drilling in typical structural thicknesses. Licensed machinists, maintenance techs, pipefitters, and HVAC fabricators routinely use cobalt bits like this for drilling carbon steel, stainless, and hard alloys where high-speed steel alone would dull prematurely.

The 5998191 is built for general-purpose metal drilling where elevated heat resistance is required. The cobalt composition of the bit maintains hardness at higher cutting temperatures compared to standard HSS, making it appropriate for drilling carbon steel, alloy steel, and similar ferrous materials. The straight cylindrical shank accepts any standard keyless or keyed drill chuck, and the right-hand spiral flute evacuates chips efficiently on conventional drill presses, hand drills, and CNC drilling centers. This bit is dimensioned and manufactured to ANSI and NAS 907 standards, making it a drop-in replacement in shops that spec tooling by those designations. It is sold individually, one piece per package.

Key Features

• Cobalt construction for elevated heat resistance when drilling steel and hard ferrous alloys
• 135-degree split point with web thinning for self-centering and reduced entry thrust
• Straw oxide finish provides lubrication and mild corrosion protection during use
• Regular right-hand spiral flute for efficient chip evacuation in through-hole and blind-hole drilling
• Straight cylindrical shank at 0.4844 inches diameter fits standard drill chucks
• Meets ANSI and NAS 907 standards for dimensional and performance consistency

Compatibility

Part of the R10CO-R15CO-R18CO series from PRECISION TWIST DRILL. Designed for drilling steel and ferrous workpiece materials. The straight shank fits any 1/2-inch or larger drill chuck on drill presses, hand drills, and CNC drilling centers. Workpiece material codes P, M, K, N, and S are supported per the manufacturer specification.

Installation Notes

Install in a properly sized chuck and confirm the shank is fully seated and centered before operating. Machinists and fabricators should apply appropriate cutting fluid when drilling steel to extend tool life and improve hole finish. Secure the workpiece firmly before drilling to prevent grab or walkout, especially at entry. Follow applicable shop safety standards and wear appropriate eye protection whenever operating drilling equipment.