What is this funny screw about?

[Muse]

Last week I did my daily skate and spotted a plastic box of screws that had evidently fallen off a truck at an intersection, most of the contents scattered around. It was a couple blocks from my house, and when I got home I bicycled over and retrieved the lot.

Several kinds of screws, some lag bolts, various sizes. Included were 47 peculiar items pictured below. They are about 3" long, have opposite threading about 3/4" down from the top and then standard threading the rest of the way. I've never seen or heard of anything like them and can't imagine what they are used for. The tool required to drive or remove them I have, which is a T20 torx.

What are they and what utility do they have?

 

[Captante]

Looks like some kind of "security" screw possibly?

 

[Muse]

Looks like some kind of "security" screw possibly?

Yeah, I'm trying to imagine how it would be implemented, what the process is.

 

[Captante]

My guess is some kind of power-drill that reverses at the top of the initial threading?

Also looks a bit like some masonry-screws (for concrete/brick) that I've seen.


EDIT: Apparently they're used in decking among other things....

Reverse Thread (RT) Trim Head Screw

 

[BoomerD]

Deck screw maybe.

Grip-Rite #9 x 2-1/2 in. Coarse Gray Internal Star Torque-Drive Composite Deck Screw (5 lb. Pack) N212CSG5 - The Home Depot

Fasten composite and polymer lumber with the #9 x 2-1/2 in. Coarse Gray Polymer-Plated Steel Square-Drive Composite Deck Screws (5 lb. Pack). These screws reduce overdriving and mushrooming with a pancake

www.homedepot.com

I prefer the Spax t-star screws for almost everything.

 

[Captante]

whoops wrong thread!

 

[Muse]

Deck screw maybe.

Grip-Rite #9 x 2-1/2 in. Coarse Gray Internal Star Torque-Drive Composite Deck Screw (5 lb. Pack) N212CSG5 - The Home Depot

Fasten composite and polymer lumber with the #9 x 2-1/2 in. Coarse Gray Polymer-Plated Steel Square-Drive Composite Deck Screws (5 lb. Pack). These screws reduce overdriving and mushrooming with a pancake

www.homedepot.com

I prefer the Spax t-star screws for almost everything.

That particular screw at Home Depot doesn't have reverse threading at the top, just different standard threading.

 

[Muse]

EDIT: Apparently they're used in decking among other things....
Reverse Thread (RT) Trim Head Screwhttps://www.decksdirect.com/rt-trim-head-screws-by-grk.html

That does definitely approximate what I have here. Gotta look it up and figure out WTH it's used for and how.

 

[Captante]

That does definitely approximate what I have here. Gotta look it up and figure out WTH it's used for and how.

Far as your SPECIFIC screw-problem I'm afraid you're on your own!

 

[BoomerD]

That particular screw at Home Depot doesn't have reverse threading at the top, just different standard threading.

Yea, I knew the threading was different, but it's for the same application....just a different manufacturer.

Of course, you can just keep looking for that exact screw and come to the conclusion that Captante and I are right.

 

[Muse]

the documentation at the link says the reverse threading at the top prevents mushrooming. I suppose that means the screw won't pop out of the deck? The reverse threads would prevent any twisting (is my thinking), although I don't know what would twist it on its own.

 

[BoomerD]

the documentation at the link says the reverse threading at the top prevents mushrooming. I suppose that means the screw won't pop out of the deck? The reverse threads would prevent any twisting (is my thinking), although I don't know what would twist it on its own.

https://solutions.dunnlumber.com/projects/composite-deck-screws-screw-products-inc

 

[herm0016]

trex screw. mushrooming is when the trex expands around the screw, the reverse thread sucks the trex surface down around the screw.

 

[shortylickens]

Those are ceramic coated for exterior use. Probably decks.
I bought some a while back for various wood projects. They're good but slightly more expensive than what normal contractors use. If you are on a budget you'll probably buy ten thousand cheap ass screws.

 

[feralkid]

They also allow for this:

https://www.lowes.com/pd/Deckorators-Pro-Plug-Hidden-Fastening-System-2-3-4-in-Dusk/5001633661

More here:

AZEK & TimberTech Decking Plugs - Fastenmaster Cortex - Starborn ProPlug

DecksDirect stocks decking plugs and plug systems for all Azek decking boards. Get the look of hidden fasteners while face fastening the decking.

www.decksdirect.com

 

[Muse]

They also allow for this:

https://www.lowes.com/pd/Deckorators-Pro-Plug-Hidden-Fastening-System-2-3-4-in-Dusk/5001633661

More here:

AZEK & TimberTech Decking Plugs - Fastenmaster Cortex - Starborn ProPlug

DecksDirect stocks decking plugs and plug systems for all Azek decking boards. Get the look of hidden fasteners while face fastening the decking.

www.decksdirect.com

Decking plugs. Yeah, I used to use those when I was working on boats at a marina. In fact, I bought a plug cutter, which I still have.

 

[nakedfrog]

That's what she said.

 

[Scarpozzi]

I saw the smaller head on that screw and thought, "That's a decking screw". I've seen a similar screw before, but it didn't have that many threads near the head.

#1 - Small head screws like that are used as finishing screws
#2 - Decking screws are typically 2.5-3" long

I'd say those work pretty well at keeping the boards tight as long as the wood isn't rotten or bad. Otherwise, they're going to be just as crappy as a standard decking screw. I used a similar screw on composite decking, but usually go with a normal phillips fastenall brand from Lowe's.

 

[BoomerD]

I saw the smaller head on that screw and thought, "That's a decking screw". I've seen a similar screw before, but it didn't have that many threads near the head.

#1 - Small head screws like that are used as finishing screws
#2 - Decking screws are typically 2.5-3" long

I'd say those work pretty well at keeping the boards tight as long as the wood isn't rotten or bad. Otherwise, they're going to be just as crappy as a standard decking screw. I used a similar screw on composite decking, but usually go with a normal phillips fastenall brand from Lowe's.

Those are made for composite (Trex) decking