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.
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.– Daniel GriscomMay 5 '18 at 20:49
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1That looks like a decking screw.– Dan D.May 6 '18 at 0:22
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@DanielGriscom what stackexchange section is good to ask about this?– skanMay 6 '18 at 0:59
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1This seems like the best place to ask– poorplanningMay 6 '18 at 3:40
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I've used screws like that for addressing squeaks in hardware floors....– BryceMay 6 '18 at 5:22
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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– MarkMay 6 '18 at 18:51
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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 '20 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) Jul 2 '20 at 6:18