jack nut

noun

A type of nut with a sheet metal body that mushrooms outward, on the far side of the hole through the substrate, when the screw is screwed in, thus providing anchoring with only one-sided access to the hole. It is nearly equivalent to the female portion of a molly bolt.

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Meanings

nounjack nut (plural jack nuts)

plural jack nuts

  1. engineeringA type of nut with a sheet metal body that mushrooms outward, on the far side of the hole through the substrate, when the screw is screwed in, thus providing anchoring with only one-sided access to the hole. It is nearly equivalent to the female portion of a molly bolt.

Origin

From the idea that the nut is jacked into its deformed (expanded) state by a jackscrew-like action of the screw. In practice this step is often performed with a tool that screws in and backs out again, and then the final mating screw follows afterward.

Full word history & related roots →
Cite this entry
APA

jack nut. (n.d.). In WatkinsX Dictionary. Retrieved November 2, 2026, from https://dictionary.watkinsx.com/word/jack%20nut

MLA

“jack nut.” WatkinsX Dictionary, https://dictionary.watkinsx.com/word/jack%20nut. Accessed November 2, 2026.

Chicago

WatkinsX Dictionary, s.v. “jack nut,” accessed November 2, 2026, https://dictionary.watkinsx.com/word/jack%20nut.

Source: jack nut on Wiktionary, CC BY-SA 4.0.