Screw extractor

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A screw extractor held in a tap wrench

The screw extractor was invented in the 1940s by Henry Lloyd Hanson, owner of H.L. Hanson a tap and die manufacturer in Worcester, Massachusetts. A screw extractor is a tool used expressly for removing broken or seized screws. There are two types; one has a spiral flute structure, which is commonly known by the trademarked name Easy Out; the other has a straight flute structure.[1] The tools are made of very hard, brittle steel; they can break off inside the screw if too much torque is applied, making the removal much more difficult.

Spiral fluted extractor[edit]

Spiral flute screw extractors

A spiral screw extractor is itself a coarse-pitched tapered screw thread. They are left-handed, for use on right-handed threads.

The screw is first drilled out to the proper diameter for that extractor. The extractor is then inserted into this hole and turned counter-clockwise using a tap wrench. As the extractor is turned the flutes on the tool dig into the screw, causing it to lock tightly and apply sufficient torque to remove the screw.[1]

A drawback to tapered screw extractors is that their wedge action tends to expand the drilled, and thus weakened, screw. This wedging action can lock the screw even more tightly in place, making it difficult or impossible to extract.

Straight fluted extractor[edit]

Square flute screw extractors

Straight fluted extractors come in a kit that also has associated drills, drill bushings, and special nuts. The screw is drilled out with the appropriate drill and drill bushing. The extractor is then hammered into the hole with a brass hammer, because a steel hammer will cause the extractor to break. The appropriate special nut is then attached to the end of the extractor. The nuts can then be turned with a wrench to remove the screw.[1]

Straight fluted extractors have less wedging effect than tapered screw extractors, so have less tendency to lock the screws into place. A further form is a parallel fluted extractor, with no taper at all and thus no wedging. These work well, but have the drawback of requiring the pilot hole to be drilled to a precise size. This size is often non-standard for most drill sets, requiring a dedicated drill bit to be supplied with the kit.

References[edit]

  1. ^ a b c Gilles, Tim (2003), Automotive service: inspection, maintenance, repair (2nd ed.), Cengage Learning, pp. 62–63, ISBN 978-1-4018-1234-8. 

Larry Barter employee of HL Hanson from 1975 - 1985