Precision Twist Drill 5998999 Cobalt Jobber Drill Bit C

Product Description

The PRECISION TWIST DRILL 5998999 is a cobalt jobber-length drill bit sized to Letter C (0.2420 inches) for heavy-duty drilling in steel and other demanding workpiece materials. The 135-degree split point starts on contact without a center punch and reduces walking on hard surfaces. Web thinning lowers thrust requirements and improves chip evacuation. An oxide and straw coating provides surface hardness and light lubricity. At 4 inches overall length with a 2.75-inch flute, the 5998999 fits standard drill chucks and delivers the reach needed for typical jobber-depth holes. Licensed machinists, maintenance mechanics, and trade professionals working in metal fabrication or mechanical service are the primary users.

This bit is suited for drilling steel, cast iron, aluminum, nonferrous metals, and high-temperature alloys, covering workpiece material codes P, M, K, N, and S. The straight cylindrical shank with 1.25-inch shank length seats in standard keyed or keyless drill chucks across benchtop drill presses, hand drills, and CNC-style equipment. The regular spiral flute geometry handles general-purpose through-hole and blind-hole applications. The 11xD flute-to-diameter ratio supports holes up to 2.75 inches deep. Series R10CO-R15CO-R18CO positions this bit in Precision Twist Drill cobalt jobber lines built to ANSI and NAS 907 standards.

Key Features

• Cobalt high-speed steel construction for heat resistance in hard and abrasive metals
• 135-degree split point with web thinning for self-starting entry and reduced thrust
• Oxide and straw coating for added surface hardness and lubricity
• Right-hand, regular spiral flute geometry for efficient chip removal
• Straight cylindrical shank fits standard drill chucks without adapters
• Meets ANSI standards and NAS 907 specification for consistent dimensional accuracy

Compatibility

Designed for use in standard drill chucks accepting a 0.2420-inch straight cylindrical shank. Compatible workpiece material codes include P, M, K, N, and S, covering carbon steels, stainless steels, cast irons, aluminum alloys, and superalloys. Part of the R10CO-R15CO-R18CO series.

Installation Notes

Secure the straight shank fully in the chuck jaws before applying power and verify the bit runs true before engaging the workpiece. Always wear eye protection and use appropriate cutting fluid or coolant when drilling steel to extend tool life and manage heat buildup. Cobalt bits are brittle compared to standard HSS — avoid side-loading or bending force. When drilling by hand, maintain steady axial pressure and reduce feed rate as the tip breaks through to prevent grabbing.