Precision Twist Drill 5997729 Cobalt Jobber Drill No. 28

Product Description

The PRECISION TWIST DRILL 5997729 is a cobalt jobber-length drill bit sized to No. 28 wire gauge (9/64 inch, 0.1406 inch decimal) designed for drilling steel and other hard workpiece materials. It features a 135-degree split point with web thinning for fast engagement and reduced walking on entry. The straw oxide finish provides light lubricity and corrosion resistance during cutting operations. At 2.875 inches overall length with a 1.75-inch flute, this is a standard jobber geometry suited for general-purpose drilling in production and maintenance environments. The straight cylindrical shank accepts standard drill chucks without any adapter.

This drill bit is intended for drilling steel, cast iron, nonferrous metals, and similar materials classified under workpiece material codes P, M, K, N, and S. It is well-suited for use in drill presses, hand drills, and CNC machining centers where a straight-shank jobber bit is specified. The heavy-duty cobalt construction makes it appropriate for harder steels and interrupted cuts where standard high-speed steel bits lose their edge prematurely. Machinists, maintenance technicians, pipefitters, and fabricators typically reach for this size when drilling pilot holes, clearance holes, or through-holes in structural steel components.

Key Features

• Cobalt construction for extended tool life in hard and abrasive steels
• 135-degree split point with web thinning reduces thrust and prevents walking
• Straw oxide finish provides light lubricity and surface protection
• Regular spiral flute geometry at 12xD ratio for efficient chip evacuation
• Straight cylindrical shank fits standard drill chucks without adapters
• Meets ANSI and NAS 907 standards for consistent dimensional accuracy

Compatibility

Part of the R10CO-R15CO-R18CO series. Designed as an OEM-style replacement or direct substitution for No. 28 wire-gauge jobber drill bits in any standard drill chuck accepting a 0.1406-inch straight shank.

Installation Notes

Secure the shank fully into the drill chuck and confirm the bit is centered before applying power. Use appropriate cutting fluid or coolant when drilling steel to extend bit life and maintain dimensional accuracy. Always wear eye protection and clamp the workpiece securely before drilling. Cobalt bits should not be run at excessively high RPM without lubrication, as heat buildup accelerates edge wear.