floggle toggle
n.— «I’ve been listening to The Navy Lark recently and noticed the writer occasional threw in some obscure but genuine naval slang for comic effect. One I’m a bit puzzled about is “floggle toggle.” It appears to be used as a placeholder name, similar to thingamajig and widget, to describe a device which if removed or incorrectly fitted will cause some some piece of equipment to fail, e.g. an engine to stop running or the ship’s guns to fire in the wrong direction.» —“Royal Navy slang” by David Bromage Usenet: alt.english.usage June 15, 2007. (source: Double-Tongued Dictionary)
Further reading
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The Floggle toggle was a part of an electrical gun firing mechanism gadget in an episode called “the gun mechanism” Series 1 ep 10
the said floggle toggle was put back on the machine the wrong way round and was used as a running joke through the show