Precision Twist Drill 5996000 Cobalt Drill Bit No. 21

Product Description

The PRECISION TWIST DRILL 5996000 is a high-performance cobalt aircraft extension drill bit designed for drilling through tough, hard, and abrasive materials including stainless steel, high-nickel alloys, and hardened steels. Built to Series CO501-6 specifications, it features a 135-degree split point that is self-centering and eliminates the need for a center punch on most surfaces. The drill measures 0.159 inches in diameter with a matching straight-cylindrical shank diameter of 0.159 inches and an overall length of 6 inches, giving it extended reach in deep-cavity and structural drilling applications. The straw oxide finish indicates proper heat treatment of the cobalt steel substrate. Licensed machinists, aerospace maintenance technicians, and industrial trades install this bit.

This extension drill bit is built for aircraft, structural fabrication, and industrial maintenance applications where standard-length bits cannot reach. The extended 6-inch overall length suits deep-hole work in airframe structures, engine mounts, and fabricated assemblies. The wire gauge size No. 21 (0.159 inches) is a common fastener clearance and rivet-hole size in aerospace and general metalworking. The bit conforms to NAS 907 Type J standards, making it appropriate for aviation maintenance and MRO operations where compliance is required.

Key Features

• 135-degree split point with self-centering geometry reduces walking and improves hole entry accuracy
• Cobalt construction provides heat resistance and hardness retention when drilling hard metals and alloys
• Web-thinned tapered web reduces thrust requirements during drilling
• 6-inch overall length provides extended reach for deep-cavity and structural applications
• Right-hand spiral flute cutting direction with 4xD flute-to-diameter ratio for efficient chip evacuation
• Conforms to NAS 907 Type J standard for aerospace and MRO use

Compatibility

Designed as an OEM-style replacement or direct-fit drill bit for applications requiring a No. 21 wire gauge size (0.159 inches) cobalt extension drill conforming to NAS 907 Type J specifications.

Installation Notes

Installation and use of this drill bit should be performed by qualified machinists, aerospace maintenance technicians, or industrial trades personnel. Secure the workpiece firmly before drilling and verify spindle speed is appropriate for the material being drilled. Use cutting fluid when drilling hardened or stainless alloys to extend tool life and maintain hole quality. Inspect the drill point for wear or chipping before each use and replace if the split point is damaged.