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I've found a screw like this. It doesn't have a whole thread, it's threaded both near the tip and near the head but not in the middle.

enter image description here

What's the purpose of this?

Furthermore the thread is partially serrated, why?

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  • Hello, and welcome to Home Improvement. My guess is that is an extremely specialized screw (especially with the small head and thread-cutting start), and doesn't have anything to do with Home Improvement. May 5, 2018 at 20:49
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    That looks like a decking screw.
    – Dan D.
    May 6, 2018 at 0:22
  • @DanielGriscom what stackexchange section is good to ask about this?
    – skan
    May 6, 2018 at 0:59
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    This seems like the best place to ask May 6, 2018 at 3:40
  • I've used screws like that for addressing squeaks in hardware floors....
    – Bryce
    May 6, 2018 at 5:22

1 Answer 1

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Doing a quick image search on Google, it looks like Dan D.’s is correct. “That looks like a decking screw.” It is also referred to as a “terrace screw.”

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  • This looks even closer, but it certainly looks like a deck screw. spaxpacific.com/products/spaxd.html
    – Mark
    May 6, 2018 at 18:51
  • OK, but there are no details about the reason of that shape?
    – skan
    May 6, 2018 at 23:48
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    The split thread is so that you can partially reverse the screw (if necessary) to even out flooring levels, i.e. if you have a low spot, then you back out the screw and the board should rise to match. I think there is usually something a little different about the top bit of thread, but maybe not on all examples/ Feb 25, 2020 at 10:15
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    @MikeBrockington - correct.. but the opposite also works.. once the thread is anchored into the frame base. the split thread enables a separation between the frame base and the board. -- often the "Fixing Thread" -- the section on the top. is slightly more compressed so that the thread ratios differ between the setting thread and the fixing thread -- Essentially presses the board harder onto the frame (preventing creaks)
    – Hightower
    Jul 2, 2020 at 6:18

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