300LH 11 PC Set

DRILLCO 300LH 11-Piece Left-Hand Cobalt Screw Machine Drill Bit Set — Engineered for Broken Bolt Extraction

The DRILLCO 300LH11 is an 11-piece left-hand cobalt screw machine drill bit set designed for counterclockwise drilling to facilitate the removal of broken bolts, screws, and other hardened fasteners. Constructed from M42 Cobalt High Speed Steel (HSS), these bits deliver superior abrasion resistance and heat tolerance compared to standard HSS drills, making them suitable for use in tough metals. The set is intended for use in left-hand screw machines and in conjunction with screw extractors, and is packaged in a rollup pouch for organized jobsite storage. Targeted at machinists, maintenance departments, contractors, mechanics, and installation crews who regularly encounter seized or broken fasteners.

Technical Specifications

Available Sizes

Unlike standard right-hand HSS drill sets, the 300LH11 combines left-hand flute geometry with M42 cobalt steel construction and a bronze surface treatment — a combination that addresses both the directional requirement for fastener extraction and the hardness demands of drilling into seized or hardened materials. The screw machine length adds rigidity that reduces deflection and breakage compared to jobber-length alternatives, and the 3-flat shank minimizes chuck slippage during high-torque counterclockwise operation.

Key Features & Benefits

M42 Cobalt High Speed Steel Construction

M42 Cobalt HSS provides superior hardness and wear resistance compared to standard HSS, enabling the bits to drill into hardened fasteners and tough metals where conventional drills would dull prematurely. Cobalt drills can drill approximately 30% faster than HSS drills, reducing cycle time on extraction jobs. Longer tool life means fewer bit replacements and lower cost per hole on demanding applications.

Left-Hand Flute and Cutting Edge Geometry

Left-handed flutes and cutting edges allow for counterclockwise drilling, which is the critical design feature for broken bolt and fastener removal. As the bit engages a broken fastener, the counterclockwise rotation can cause the fastener to back out on its own without requiring a separate extractor. This geometry makes the set directly compatible with left-hand screw machines and screw extractor workflows.

135° Self-Centering Split-Point

The 135° split-point is self-centering, which reduces walking when starting a hole on a flat or curved surface and minimizes the thrust force required to begin cutting. For extraction work where precise hole placement over a broken fastener is essential, this point geometry improves accuracy and reduces the risk of damaging the surrounding material.

Bronze Surface Treatment

The bronze surface treatment increases lubricity at the cutting interface, reducing friction and heat buildup during drilling. This protective layer extends tool life and helps manage chip buildup, which is particularly important when drilling into harder metals and stainless steel. Reduced heat at the cutting edge also helps preserve the cobalt steel's hardness over repeated use.

Screw Machine Length for Added Rigidity

The shorter screw machine length increases the rigidity of each bit compared to jobber or taper length drills, directly reducing the risk of deflection and breakage during high-torque extraction operations. Greater rigidity also improves hole accuracy, which is important when drilling concentrically over a broken fastener stub.

3-Flat Shank for Reduced Chuck Slippage

The 3-flat shank design (on sizes 3/16" and above) provides positive engagement in the drill chuck, preventing the bit from rotating within the chuck under the high torque loads typical of counterclockwise extraction drilling. This reduces operator frustration and prevents damage to both the chuck and the shank.

Common Applications

Broken Bolt Removal

The primary application for this set is drilling out broken bolts using counterclockwise rotation, which can cause the fastener to back out as the bit engages it. The cobalt construction handles the hardened steel typically found in seized or heat-affected fasteners.

Use with Screw Extractors

The 300LH11 is designed for use in conjunction with screw extractors, where the left-hand drill first creates a pilot hole in the broken fastener before the extractor is applied. The 11 sizes cover the most frequently encountered fastener diameters in this workflow.

Left-Hand Screw Machine Operations

These bits are suited for use in left-hand screw machines where counterclockwise spindle rotation is standard. The screw machine length and 3-flat shank are optimized for this type of equipment.

Drilling Hardened Fasteners and Tough Metals

The M42 cobalt HSS material makes these bits capable of drilling into hardened materials that would quickly dull standard HSS bits, including high-tensile fasteners and hard alloy steels encountered in maintenance and repair work.

Maintenance and Repair Applications

Maintenance departments, mechanics, and installation crews use this set for field and shop repair situations where broken or seized fasteners must be removed without damaging the surrounding workpiece. The rollup pouch keeps all 11 sizes organized and accessible on the job.

Compatible Materials

• Hardened metals
• Tough metals (general)
• Hardened fasteners (broken bolts, screws)

Product Documents

• Safety Data Sheet (SDS)
• Product Sheet
• Linecard

Safety Data Summary

Hazard Information

• During normal operation, cobalt cutting tools do not present inhalation, ingestion, or other chemical hazards.
• Grinding, cutting, machining, burning, or welding may release dusts, fumes, or vapors that present health hazards if exposure limits are exceeded.
• Excessive inhalation of metallic fumes and dusts may cause irritation of eyes, nose, and throat.
• High concentrations of fumes and dusts of iron oxide, manganese, copper, zinc, and lead may result in metal fume fever (metallic taste, throat irritation, chills, fever — symptoms may persist 12 to 48 hours).
• Cobalt is listed as a Group 2B carcinogen by IARC (possibly carcinogenic to humans). Chromium and Nickel are listed as carcinogens by NTP and OSHA.
• Chronic exposure to cobalt dusts, fumes, and mists may cause permanent respiratory diseases including occupational asthma, interstitial pneumonitis and fibrosis (hard-metal disease), and emphysema.
• Skin sensitization to cobalt is noted in a small percentage of cases.
• Fine metal particles produced when ground or sawed can burn; high concentrations in air may present an explosion hazard.
• NFPA Hazard Rating: Health 1; Flammability 0; Reactivity 0.
• California Proposition 65 Warning: This product can expose you to chemicals including Cobalt, which is known to the State of California to cause cancer. For more information go to www.P65Warnings.ca.gov.

Personal Protective Equipment

• Wear safety glasses or goggles with side shields; do not wear contact lenses when handling.
• Cloth or leather gloves recommended when contact with dust or mist is likely.
• Use an appropriate NIOSH-approved respirator if airborne dust concentration exceeds the applicable PEL or TLV.
• Hearing protection may be required.
• Always use machine guards and wear protective clothing to prevent injury in the event of tool breakage.
• Employer should provide an eye wash station within the immediate work area.

Safe Handling

• Use only with local exhaust ventilation adequate to limit personal exposure to airborne dust below PEL or TLV levels.
• All grinding, welding, or fume-generating operations should be performed in well-ventilated areas.
• Clean up using methods that avoid dust generation: vacuum with appropriate filters, wet dust mop, or wet clean-up.
• Wash hands thoroughly after handling and before eating or smoking; wash exposed skin at end of work shift.
• Do not shake clothing, rags, or other items to remove dust — remove dust by washing or vacuuming with appropriate filters.
• Store in a dry place in a manner that prevents accidental environmental contamination from traces of industrial lubricants or wetting oils.
• Soiled clothing should be laundered separately.
• Incompatible with strong acids and strong oxidizers.
• For powder fires: smother with dry sand, dry dolomite, ABC-type fire extinguisher, or flood with water.
• Emergency phone: CHEM-TEL INC 1-800-255-3924.

Frequently Asked Questions

Q: What is the primary purpose of this left-hand drill bit set?
A: The 300LH11 is designed for counterclockwise drilling to facilitate the easy removal of broken bolts, screws, and other hardened fasteners. It is used in left-hand screw machines and in conjunction with screw extractors.

Q: Why use cobalt HSS instead of standard HSS for this application?
A: M42 Cobalt HSS provides superior abrasion resistance and hardness compared to standard HSS, making it capable of drilling into hardened materials. Cobalt drills can drill approximately 30% faster than HSS drills, and they offer longer tool life in tough metals.

Q: What sizes are included in the 11-piece set?
A: The kit contains the 11 most frequently used sizes: 1/16", 3/32", 1/8", 5/32", 3/16", 7/32", 1/4", 9/32", 5/16", 11/32", and 3/8".

Q: Does the 3-flat shank apply to all sizes in the set?
A: The 3-flat shank for reduced slippage in the drill chuck applies to sizes 3/16" and above. Smaller sizes below 3/16" have a standard round shank.

Q: Why is screw machine length used instead of jobber length?
A: The shorter screw machine length adds rigidity to the drill bit, which reduces deflection and breakage — particularly important during the high-torque counterclockwise drilling required for fastener extraction.

Q: What are the critical factors for getting the best performance from these bits?
A: According to DRILLCO, speed, feed, and lubrication are all critical to cutting tool performance. Proper attention to all three parameters will maximize tool life and cutting efficiency.