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I scavenged an old bolt from an interior office remodel, and it is odd.

The thread appears to be triple-start BUT two of the three are milled off.

Shaft is 11.8mm and appears to be galvanised but the missing threads are shiny so appear to be trimmed after galvanising.

Pitch of threads is about 8.9 mm / turn to the same crest, so presumably 3.0 mm between adjacent crests if they were there.

There is a slight taper to the tip, and the threads also have a tapered lead-in. The crest of the remaining thread seems to have intentional "divots" every 60 degrees for the first rotation, but they don't look like cutting teeth.

The head is a 6 sided hex with a flange. The work was inside, so not exposed to any weather.

What is the purpose of this thread ?

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Criggie
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1 Answers1

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It is a screw that cuts its own threads in concrete.

Drill a hole in concrete and then use a wrench to screw it in.

Follow the manufacturer's directions as to the diameter and depth of the hole.

Internet image search reveals that it is possibly an AM Premium Concrete Screw, because of the triple thread.

jsotola
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