Precision Twist Drill 5998156 Cobalt Jobber Drill 21/64 in

Product Description

The PRECISION TWIST DRILL 5998156 is a cobalt high-speed steel jobber-length drill bit designed for demanding metal-cutting applications. It features a 135-degree split-point geometry with web thinning, which reduces walking on entry and lowers thrust force compared to a conventional 118-degree point. The straw oxide finish provides mild lubricity and heat resistance during drilling. At 21/64 inches (0.3281 inches) in diameter with a 4.625-inch overall length and a 3.3125-inch flute length, this bit suits production and maintenance drilling in steel, cast iron, aluminum, and high-temp alloys. Licensed trades and industrial machinists install this bit in standard drill presses, CNC machines, and hand-held power drills.

This jobber drill is built for general-purpose heavy-duty drilling in ferrous and non-ferrous materials. It carries a Primary Workpiece Material Code covering steel, stainless, cast iron, aluminum, and superalloys (P, M, K, N, S classifications). The regular spiral flute with a 10xD flute-to-diameter ratio provides efficient chip evacuation in through-hole and blind-hole applications. The straight cylindrical shank accepts standard drill chucks without an adapter. It is suitable for residential and commercial fabrication shops, HVAC equipment assembly, plumbing rough-in, and general sheet-metal or structural steel work.

Key Features

• Cobalt high-speed steel construction for improved heat and wear resistance in hard materials
• 135-degree split point with web thinning reduces thrust and self-centers on entry
• Straw oxide finish provides light lubricity and corrosion protection
• Regular spiral flute with tapered web geometry for consistent chip evacuation
• Straight cylindrical shank fits standard 3-jaw drill chucks without adapters
• Meets ANSI and NAS 907 standards for dimensional accuracy and material grade

Compatibility

Part of the PRECISION TWIST DRILL Series R10CO-R15CO-R18CO cobalt jobber drill line. Designed as an OEM-style replacement or direct addition for any application requiring a 21/64-inch straight-shank jobber drill in steel, stainless, cast iron, aluminum, non-ferrous, or high-temp alloy workpieces per NAS 907 and ANSI specifications.

Installation Notes

Install in a drill press, CNC spindle, or hand-held drill with a properly sized 3-jaw chuck, ensuring the shank is fully seated and the chuck key is removed before operation. This bit is not designed for coolant-through use. Secure workpieces firmly before drilling to prevent bit deflection or breakage. Always wear appropriate eye protection and follow applicable shop safety codes when operating rotary cutting tools.