Replacing Screws

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3 Oct 2018
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Currently helping convert a horse box into a studio flat on wheels. There are about 600 screws that we are pulling out of the sapele planks which make up the box, which screw into the ash frame. They're imperial screws of 5.5x55mm ish so i assume a 6mmx60mm replacement would be fine. The heads are not going to be visible in the finished project and the screws will be replaced as many are rusted/broken.

I have always found screwing into hardwood surprisingly difficult, and in my joinery don't tend to use screws beyond hinges etc. I wonder whether you guys think there is any reason not use a screw like this:
Are stainless steel screws a good idea for this project, or is the above fine? Must I use a partially threaded screw or would a fully threaded screw - i assume a partial thread is a must to pull the boards back on tight?

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I'll leave others, better qualified to answer your question. But I'd love to see photos of the finished project, sounds like a lot of fun, if my daughter heard of this I bet she'd want one for festivals!
Those long but thin pozis, and SS, break easily as they go deeper against resistance, so have to be drilled out for, very carefully.
Full size loose fitting hole for the planks and a precise hole for the ash.
No point in full thread through the planks
Thing is - i'm not sure a 60x6mm pozi screw can be considered particularly long and thin? They will be going back into the holes that were drilled before.
I'd agree with you, 0.5mm thicker and 5mm longer they should go in easily, you may even need to pack out some of the holes if the rust has expanded them or you damage getting rusted screws out. Those cheap screws can snap without warning so do need care though I've had it happen only on rare occasions and always my own fault.
Personally I'd use stainless on a job like that, more expensive but surely a small amount in the over all conversion costs.

Whichever screws you use, dipping in wax / furniture polish will make the job a lot easier
If cost is not a problem, you're suffering from rust now, so expect it in future so stainless would be of benefit
longer term? 6x60 posi would have an advantage. As would an impact driver with so many!
^^^ as Jacob said, make you have clearance in the holes in the boards - the full thread doesn't matter then.
Use Reisser, Spax or another good brand of screw to minimise the chances of their breaking.
S/S is ideal, but modern coated screws won't rust anything like as quickly as old mild steel ones.
I'd just go with normal screws if is interior cladding then they loads are going to be minimal and corrosion isn't going to be a great problem certainly less than when it was a horse box?

The cost of that number of SS screws is going to be expensive.

Any more questions just ask.

I lurk in the motorhome fun site a bit too, so see quite a few conversions although most are boring PVC rather than your characterfull horsebox.

Any pics

Cheers James
You say appearance doesn’t matter as they won’t be seen, I wouldn’t even try and take the old ones out, just go up and down drilling fresh holes first of all with a depth stop so that you only do a clearance hole through the plank itself then go around again and drill a bit deeper for a pilot hole if you think it’s necessary,
OK chaps, that is good advice. Going to biff the stainless steel ones off. I'll post some pictures and start a thread for the horsebox conversion soon.