Screw extractor ELORA 350 for broken bolts M3-M50, pilot hole 2.5-21 mm

Screw extractor for broken bolts ELORA 350 removes fasteners from M3 to M50 (1/8 to 2 inch) using reverse-thread engagement. Each extractor in the series matches a specific bolt-size range. Pilot-hole diameter must be chosen precisely to avoid extractor fracture or thread damage. The series includes eight models with shank diameters from 3.95 mm to 25 mm.

Correct pilot-hole selection is critical. An undersized hole risks breaking the extractor. An oversized hole removes too much bolt material and weakens thread engagement. The table below maps each model to its recommended pilot-hole diameter.

Screw Extractor for Broken Bolts: Operating Principle

The tool uses left-hand threads cut into a tapered body. After drilling a pilot hole into the broken stud, the extractor is turned counter-clockwise. The reverse thread bites into the remaining bolt material and unscrews it from the threaded hole. This method works when the bolt head has sheared off flush or below the surface.

Model Range and Pilot-Hole Requirements

Eight extractors cover the full M3–M50 range. Each model specifies tip diameter, shank diameter, applicable bolt sizes, and required pilot-hole diameter. Matching the correct extractor to the broken bolt size ensures safe removal without damaging the parent thread.

• Model 350-6: tip 1.75 mm, shank 3.95 mm, M3–M6 (1/8–1/4 inch), pilot hole 2.5 mm (3/32 inch)
• Model 350-8: tip 2.2 mm, shank 4.8 mm, M6–M8 (1/4–5/16 inch), pilot hole 3 mm (1/8 inch)
• Model 350-11: tip 3.3 mm, shank 6.4 mm, M8–M11 (5/16–7/16 inch), pilot hole 4.5 mm (11/64 inch)
• Model 350-14: tip 4.75 mm, shank 8.4 mm, M11–M14 (7/16–9/16 inch), pilot hole 6 mm (15/64 inch)
• Model 350-18: tip 6.35 mm, shank 11 mm, M14–M18 (9/16–3/4 inch), pilot hole 8 mm (5/16 inch)
• Model 350-24: tip 9.5 mm, shank 15 mm, M18–M24 (3/4–1 inch), pilot hole 11 mm (7/16 inch)
• Model 350-33: tip 12.7 mm, shank 19 mm, M24–M33 (1–1.3/8 inch), pilot hole 14 mm (9/16 inch)
• Model 350-52: tip 19 mm, shank 25 mm, M33–M50 (1.3/8–2 inch), pilot hole 21 mm (53/64 inch)

Each extractor is manufactured from tool steel. The tapered geometry and reverse-thread profile are machined to tight tolerances. This construction minimizes the risk of extractor breakage during use and protects the parent thread from further damage.

Pilot-Hole Drilling Procedure

Before inserting the extractor, drill a pilot hole centered on the broken bolt. Use a drill bit diameter that matches the recommendation for the chosen extractor model. Drill to a depth slightly greater than the length of the broken stud. Remove all chips and debris from the hole before inserting the extractor.

• Center-punch the broken bolt to guide the drill bit
• Select the drill diameter from the model table
• Drill perpendicular to the surface to avoid off-center holes
• Clear chips frequently to prevent bit binding
• Verify hole depth exceeds the stud length

Accurate centering and correct drill size are essential. An off-center hole will cause the extractor to bind or break. An incorrect diameter will either fracture the extractor or leave insufficient bolt material for the reverse thread to grip.

Common Applications

This extractor series is used in automotive repair, machinery maintenance, and general metalworking. Typical scenarios include removing broken exhaust studs, cylinder-head bolts, and fasteners seized in aluminum or cast-iron housings. The tool is also employed in field service where access to welding or other heat-based removal methods is limited.

Selection and Use Guidelines

Identify the nominal size of the broken bolt. Consult the model table to select the correct extractor and pilot-hole diameter. Drill the pilot hole carefully, ensuring it is centered and perpendicular. Insert the extractor and turn counter-clockwise with steady pressure. Avoid excessive force, which can snap the extractor.

• Measure or identify the original bolt size
• Match the bolt size to the extractor model range
• Drill the pilot hole to the specified diameter
• Insert the extractor fully into the pilot hole
• Turn counter-clockwise with controlled torque
• If resistance is high, apply penetrating oil and retry

The ELORA 350 series is manufactured in Germany. Each extractor is marked with its model code and size range. The tools are supplied individually, allowing users to purchase only the sizes required for their specific repair tasks.