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A screw I have not come across before - Decking

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Geoff_S

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We are fitting some composite decking provided by a company called Silvadec, who have no UK support, we now find out.

They have some coloured composite screws to match the decking so we thought we would use them!

Well, they are a bit strange. They are RH thread on the bottom bit, a smooth collar, then LH thread at the top!

The idea was to screw down decking boards with them, but we cannot figure out how they work. As you screw them through the board, as the top thread bites, it pushes the decking board up.

The supplier isn't much help either!

Any ideas?

IMG_1624.jpeg
 

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eezageeza

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It looks the same as a lost tite screw - might be worth a google to see if there's some explanations of how they work
 

Phil Pascoe

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I would think the top thread would strip the thread just cut by the bottom one ............ but if that's the object why not just a screw with a smaller, plain shank? :?
Email the manufacturer?
 

sammy.se

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From the link I posted:

"It does work like that, but not when you first punch the screw down, what happens with these is, the bottom of the threads is wider than the top, and the top just spins in the decking, but after getting some sun a couple times the composite expands (which shrinks the hole size) and that grabs the threads. After which, they are a total puppy to remove as they have become locked. Works on really dry wood too, after getting wet once they lock in place."
 

Geoff_S

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Thanks guys. The Reddit thread makes sense, but the diameter of both threads is the same, and longer at the top than the Screfix ones. It's
a mystery :?
 

Desi2ie

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I can’t post a link but if you google silvadec screws there is a site beginning with uk that has installation instructions in its documentation section not a lot to say on the screw fixings except 3.5 mm pilot hole essential might be of some use anyhow
 
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