Screw size and drill bit size

[Clariman]

I have had some Italian bedroom furniture delivered which is already assembled, except for some screw in feet and a top panel. The carcase already has a functional top but the panel is for finish.

There are no holes in the finishing panel, but the functional top has 4 pilot holes which I need to drill. I then screw up through the drilled holes into the finishing panel to attach it on. At least I am 99% certain that is what the picture instructions are telling me to do.

What is confusing me is the screw specification and the drill bit required. The screws, which are provided, are described as 3.5x25 tsp which I think means they are 3.5mm in diameter.

The drill bit is described as Ø5. I don't understand what is meant by the Ø. If it is a slashed zero just meaning 0, then it is superfluous. Besides if that meant the drill bit was 5mm surely that would be too big for a 3.5mm screw? I also notice that the the Ø is a perfect circle rather than a number - a bit like a null set sign. What does it mean here in connection with a drill bit in these instructions?

Thanks
C

[Urbandreamer]

What is confusing me is the screw specification and the drill bit required. The screws, which are provided, are described as 3.5x25 tsp which I think means they are 3.5mm in diameter.

The drill bit is described as Ø5. I don't understand what is meant by the Ø. If it is a slashed zero just meaning 0, then it is superfluous. Besides if that meant the drill bit was 5mm surely that would be too big for a 3.5mm screw? I also notice that the the Ø is a perfect circle rather than a number - a bit like a null set sign. What does it mean here in connection with a drill bit in these instructions?

Thanks
C

It sounds odd to me. However to answer about Ø, it usually means diameter or OD (outside diameter). They might mean a number 5 drill bit, which is slightly bigger than 5mm.
It should be easy to get a rough size for the screws with a rule.

It is also worth pointing out that when joining two things with a screw, the hole in one is usually clearance. That is the screw will easily pass through it without biting. This is so that the screw can pull the two parts together.

[monabri]

Could it be a typo and should read "diameter 3mm" ? (surely a 3m diam hole is more suited to a 3.5mm self tapper?)

A 5mm hole would surely be too big..try drilling a 5mm diam hole in a scrap piece of wood and see how secure it is(n't)!

Then try the same screw on a 3mm diam hole in a scrap piece of wood.

You'll be able to judge if a 3mm diam drill is the one to go for!

The screw is 25mm long threadwise, I'd check/confirm that the furniture can accommodate that length of screw first!!

[BullDog]

The slashed zero ("0" or "O") is shorthand for diameter.
I'm not entirely clear what is being done here. If there's two pieces, one screwed on top of another. Then the piece of wood under the screw head may well need a 5mm hole for clearance on the 3.5mm screw. The actual thread length of the screw being screwed into the piece underneath, obviously not a clearance hole there.

[jfgw]

How big are the screw heads? 5mm seems a big clearance hole for a screw size that typically has a 7mm diameter head. What sort of wood?

I don't know who uses number and letter gauge drills now. Maybe old model engineers and clock makers. I have most sizes but I rarely use them.


Julian F. G. W.

[Clariman]

I think perhaps the the 5mm drill bit means the screw will pass through the carcass cleanly and then screw into the top? I've sent a message to the supplier to ask them some specific questions about it. No wonder they normally sell this stuff as part of a fitted bedroom that they install

[quelquod]

I think perhaps the the 5mm drill bit means the screw will pass through the carcass cleanly and then screw into the top? I've sent a message to the supplier to ask them some specific questions about it. No wonder they normally sell this stuff as part of a fitted bedroom that they install

As said, the Ø usually denotes outside diameter so a 5mm drill here. Regarding the oversize that @jfgw mentions it’s difficult to say without actually seeing it but it sounds as though there’s intended to be a bit of slack to perhaps allow the top to be perfectly aligned before final tightening. I’d be inclined to run a smaller drill right through and into the top first (not right through!) to help alignment and closer fitting.

[DrFfybes]

I tend to drill a pilot hole 0.5mm wider than the screw size, although a bit wider isn't an issue.

A 3.5mm screw usually takes a no2 screwriver bit, either pozi or phillips (and occasionally JIS), usually the one you haven't got to hand.

Paul

[Urbandreamer]

A 3.5mm screw usually takes a no2 screwriver bit, either pozi or phillips (and occasionally JIS), usually the one you haven't got to hand.

Paul

Please, please don't get me started on screwdrivers. The number of people who don't understand that there ARE different types and sizes. Or that using the wrong one doesn't work or can make things worse!

Ps, I'd disagree about the comment "usually". My experience was that, where I worked, a hex driver or torx driver were more common. But they were not wood screws.

[servodude]

I think perhaps the the 5mm drill bit means the screw will pass through the carcass cleanly and then screw into the top? I've sent a message to the supplier to ask them some specific questions about it. No wonder they normally sell this stuff as part of a fitted bedroom that they install

That would be the "normal" way to fit some tops in my experience; it makes it easier to get everything in the right place once installed, especially if you need to move anything.
Helps deal with the fact floors and walls are rarely true.

Often it's done with a recessed pan head rather than countersunk screw