Hertel 04139390 Cobalt Jobber Drill Bit Letter L

Product Description

The HERTEL 04139390 is a cobalt jobber-length drill bit sized to Letter L (0.2900 inches decimal), designed for heavy-duty holemaking in ferrous and difficult-to-machine materials. It features a 135-degree split point that reduces walking at startup and lowers thrust force during entry. The oxide and TiN coating improves surface hardness and extends tool life in production drilling environments. With an overall length of 4.25 inches and a flute length of 2.9375 inches, this is a standard jobber-series geometry suited for use in drill presses, CNC machining centers, and hand-held pneumatic or electric drills. Licensed machinists, millwrights, pipefitters, and maintenance technicians are the typical users.

This bit is appropriate for production and maintenance drilling operations where a right-hand, regular-spiral, straight-cylindrical shank drill is required. The 0.2900-inch shank diameter matches the cutting diameter for direct chuck mounting without adapters. Its heavy-duty cobalt grade handles interrupted cuts, stainless steel, high-nickel alloys, and hardened steel better than standard high-speed steel bits. The web-thinned, tapered-web configuration reduces cutting resistance at the chisel edge, making it practical for both manual and automated feed applications.

Key Features

• Letter L size: 0.2900 inches decimal diameter for precise hole sizing
• 135-degree split point reduces thrust and eliminates center-punch requirement on most materials
• Cobalt construction with oxide and TiN coating for extended wear resistance in hard and abrasive materials
• Web-thinned, tapered-web design lowers cutting torque and improves chip evacuation
• Right-hand, regular-spiral flute geometry for standard clockwise-rotation drilling
• Straight-cylindrical shank fits standard 3-jaw drill chucks without sleeves or adapters

Compatibility

Designed as a standard jobber-series drill bit for use in any drill press, lathe tailstock, or hand-held drill accepting a straight-cylindrical shank in the 0.2500 to 0.3000 inch diameter range.

Installation Notes

De-energize or lock out all rotating machinery before changing tooling, following applicable OSHA lockout/tagout procedures. Verify chuck jaw condition and tighten fully before operation to prevent bit slippage. Coolant-through is not supported on this bit; apply cutting fluid externally when drilling stainless, high-alloy steels, or other work-hardening materials. Inspect cutting edges for chipping or wear before each use and replace when point geometry is compromised to avoid work-hardening the bore.